Is this homebrew Dragon Rider class balanced compared to the other official classes?

Question

Is this homebrew Dragon Rider class balanced compared to the other official classes in 5e?

Note that all the spells I've put on the Rider spell list require concentration.

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The class:

Dragon Rider

Dragons terrify most adventurers, but for you, one very small dragon decided to bond with you, giving you the gift of magic as well. Why did the dragon choose you? Did your country or city test every citizen for a bond? Did you find your dragon still in an egg while exploring a abandoned dragon cave far greater adventurers cleared years before? Did you stumble upon it in the woods one day while hunting? Are the dragon's parents or a military looking for it?

Quick Build:

Intelligence should be your highest score as a Rider, followed by Constitution or Strength/Dexterity. Get starting equipment (c) and choose the spells Faerie Fire, Hunter's Mark, Arcane Weapon, and Thunderous Smite.

Dragon Rider Spell List

1st-level

Arcane Weapon
Ensnaring Strike
Entangle
Expeditious Retreat
Faerie Fire
Fog Cloud
Hail of Thorns
Hunter's Mark
Searing Smite
Thunderous Smite
Wrathful Smite
Zephyr Strike

2nd-level

Alter Self
Blur
Branding Smite
Earthbind
Magic Weapon
Silence
Skywrite
Warding Wind

3rd-level

Blinding Smite
Call Lightning
Crusader's Mantle
Elemental Weapon
Flame Arrows
Lightning Arrow
Protection from Energy
Vampiric Touch

4th-level

Elemental Bane
Grasping Vine
Greater Invisibility
Staggering Smite
Storm Sphere

5th-level

Animate Objects
Antilife Shell
Circle of Power
Control Winds
Far Step
Immolation
Telekinesis

Class Features

Hit Points

Hit Dice: 1d8 per Dragon Rider level
Hit Points at 1st level: 8 + your Constitution modifier
Hit Points at Higher Levels: 1d8 (or 5) + your Constitution modifier for each Dragon Rider level after 1st

Proficiencies

Armor: Light Armor and Shields
Weapons: Simple and Martial Weapons
Saving Throws: Intelligence and Constitution
Skills: Choose 3 skills from Perception, Arcana, Nature, Medicine, History, Animal Handling, and Acrobatics
Tools: Leatherworker's Tools, Dragonchess Set

Equipment

You start with the following equipment, in addition to the equipment granted by your background:

• (a) a greatsword; (b) a longsword, 6 javelins, and a shield; or (c) a rapier, a longbow, a quiver with 20 arrows, and a shield

• leather armor, an explorer's pack, and a leatherworker's kit.

Dragon Bond

When you take you first level in this class, you gain a pseudodragon companion with a permanent telepathic bond to you. You always know the location of your dragon as long as it is in the same plane as you. You and this dragon can read and speak Draconic, and you can communicate with each other at a distance of a number of miles equal to your level. As an action, you can see through your dragon's eyes.

If your dragon is killed, you suffer one level of exhaustion from the stress of having your telepathic bond severed. You can spend a long rest to bring it back to life. If you do this, you end your long rest with 0 mana points.

Spellcasting

Unlike other spellcasters, your magic comes from the power your dragon bestowed on you when you met it; thus, you have no spell slots. Instead, you have a maximum amount of mana equal to your Rider level. You regain all expended mana on a long rest. Whenever you cast a spell, you can spend 1 additional mana to cast it as if you were in your dragon's location.

Intelligence is your spellcasting modifier for Rider spells. You know 4 Rider spells from the Rider spell list and learn 1 more whenever you gain a level in this class.

When you cast a Rider spell, you spend mana according to the table below. If you do not have enough mana, you cannot cast the spell.

\begin{array}{cl} \textbf{Spell Level} & \textbf{Mana Cost} \\ \text{1st} & \text{1 Mana}\\ \text{2nd} & \text{3 Mana}\\ \text{3rd} & \text{5 Mana}\\ \text{4th} & \text{7 Mana}\\ \text{5th} & \text{9 Mana} \end{array}

Fighting Style

At level 2, choose between the Two-Weapon Fighting, Archery, Defense, Great Weapon Fighting, Dueling, or Mariner fighting styles. You can't benefit from the same fighting style more than once.

Mastery

At level 3, choose between the Spell Master and Weapon Master subclasses.

Ability Score Improvement

When you reach 4th level, and again at 8th, 12th, 16th, and 19th level, you can increase one ability score of your choice by 2, or you can increase two ability scores of your choice by 1. As normal, you can’t increase an ability score above 20 using this feature.

Using the optional feats rule, you can forgo taking this feature to take a feat of your choice instead.

Draconic Growth

At level 5, your pseudodragon grows up into a wyrmling of any color of your choice except red. No one (including you) can ride your wyrmling. Your wyrmling can only use its breath weapon once per short rest, unless it has multiple breath weapons, in which case it can only use each option once per long rest.

Improved Bond

At level 6, once per short rest, whenever you take damage, you can use your reaction to have your dragon take the damage instead. Additionally, once per short rest, your dragon can use its reaction whenever it takes damage for you to take the damage instead. Transferred damage cannot be reduced in any way.

Additionally, you automatically succeed on any saving throw against your dragon's breath weapon.

Draconic Tendencies

At level 9, your bond with your dragon begins to influence you. You gain proficiency in the Survival and Nature skills, your eyes continuously glow the color of your dragon, and you learn the Thaumaturgy cantrip.

Draconic Growth

At level 10, your dragon grows into a young dragon of the same color as it was as a wyrmling. One Medium creature or two Small creatures can ride on your dragon at a time. It still has the same breath weapon limitations as before.

Extra Attack

Beginning at 11th level, you can attack twice, instead of once, whenever you take the Attack action on your turn.

Riding Master

At level 13, you have advantage on saving throws you make to stay on your dragon while it is in flight.

Greater Bond

At level 15, when a creature takes damage from your dragon's breath weapon, that creature has disadvantage on saving throws it makes against your Rider spells until the end of your next turn.

Increased Draconic Tendencies

At level 17, you stop aging and can't be aged magically. You are immune to disease.

Draconic Growth

At level 20, your dragon grows into an adult dragon of its color. 3 Medium or 6 Small creatures can now ride it at a time, and it is no longer is limited in uses of its breath weapon.

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Subclasses

Weapon Master

At level 3, when your dragon makes a critical hit on a creature, you have advantage on attacks against that creature until the end of your next turn.

At level 7, when you use your action to cast a spell, you can make one weapon attack as a bonus action.

At level 18, your ranged attacks are made at advantage while you are riding your dragon. In addition, if you move towards a creature at least 60 feet in a round, your first attack against that creature before the end of your next turn does an extra 4d10 piercing damage if it hits.

Spell Master

At level 3, you regain mana points equal to your proficiency bonus whenever you complete a short rest.

At level 7, you can use a bonus action to spend mana points and give yourself or your dragon hit points equal to the 5 times the mana points you spend.

At level 18, you learn one 6th-level spell and one 7th-level spell from the sorcerer spell list, and can cast each of these once per long rest.

Answer 1

No

Let's take this feature at a time...

Quick build

This is just flatly wrong. This class is a half-caster, they should not prioritize their casting stat. Glancing down below, this class would always want to prioritize Dex--they are restricted to Light Armor no access to the Mage Armor spell and they don't have Cantrips for steady damage output. So they'll want a high Dex for AC, and to make use of Ranged or Finesse weapons--Str is not a good primary for a class that is restricted to Light Armor.

Proficiencies

Light armor only? This pigeonholes this class into a Dex-build if they want anything resembling durability. They are not a dedicated caster--don't even have Cantrips.

Draconic bond.

Basically a Familiar that can attack at this point. However, unlike a Chain Warlock's familiar, the Pseudodragon does not consume one of your attacks in order to act--as-written, this is a complete secondary character.

Spellcasting

You have the spell range of a half-caster, but weirdly scaling efficiency. Without playtesting, it would be hard to determine how this pans out.

That said, your spell list is basically a grab-bag of the most useful spells in the game drawn from every class's list. Balanced fairly well by the fact that they are mostly (all?) Concentration spells

As an aside--you need to rename this feature. Classes that don't follow the standard rules for spellcasting call their magic feature something else--like a Warlock's Pact Magic.

Fighting Style

You get the same full range of fighting style options as a Fighter does. There is basically precedent for this with a Paladin.

ASI

Normal, whatever, moving on.

Draconic Growth

And here is where the balance starts its nose-dive. Assuming you take a Blue or Gold dragon, you just added a CR 3 companion. At a rough ballpark based on experience, a CR 3 monster is roughly the equivalent of a 4th to 5th level character in combat. So, at 5th level, you are basically controlling 2 characters of roughly similar combat effectiveness.

For comparison, the wolf of a 5th level Beast Master ranger has 1 less AC, 1/3 the HP, and does a fair bit less damage while attacking. And, most importantly A ranger must give up an attack of their own to let their wolf attack. And that's not including the dragon's breath weapon.

I would also note that about this point--your 'pet' is lining up to be as good at Persuasion as your party's social lead unless you have someone with Expertise in Social Skills

Improved Bond

Seems handy in a pinch...not a huge deal, moving on.

Draconic Tendencies

Again, not a huge deal...but I would note there's nothing in there about what to do if you already have the Survival and Nature skills

Draconic Growth

So, the wyrmlings usefulness has gradually been tapering off and keeping it alive has gotten hard. That's gone again.

Assuming you went for optimization and took a Gold Dragon...you are now a level 10 player with a CR 10 companion. Again, based on experience, I ballpark that a CR 10 monster is at least on-par with a level 14 PC. Now you have a pet dropping three (very powerful) attacks per round, as well as their breath weapon--and almost certainly has more hp than your party's Barbarian.

Extra attack

So...now your character is up to 5 effective attacks per round? 2 from themselves, 3 from their Dragon.

Riding Master

A fragment of the Mounted Combatant feat...moving on

Greater Bond

I can see this stacking in pretty terrifying ways. It will always work unless aimed at a creature with Evasion.

Increased Draconic Tendencies

Fluff, moving on

Draconic Growth

Ah-hahahahahahahahahahahahahahahaha

Why are you still in a party? You have a CR 17 companion (significantly more powerful than a level 20 PC) that has Legendary Actions and Legendary Resistance. Other classes get a 4th Attack or regenerating class resources--but you? You get a pet legendary monster.

Subclasses

Weapon Master

Level 3
Seems niche and kinda weird..whatever

Level 7
Eldritch Knights don't get this until level 18

Level 18
Stronger than the Mounted Combatant feat, and that's some pretty serious damage...

Spell Master

Level 3
Okay, now you're almost a half-caster. Still really inefficient

Level 7
The lack of a range on this is questionable--otherwise this doesn't seem too out of place

Level 18
Again, pretty potent, but not nearly as broken as your pet flying apocalypse.

Summary

You have a boss monster as a free-acting companion. There is no possible way this is balanced against the core classes unless the storyline gives them some way to acquire creatures of similar power. Which you could do, of course--but that's not what you asked.

Ultimately, the character themselves is quite lackluster--with underpowered spellcasting, no extra attack until level 11, and being stuck in light armor.

However, they have a boss monster as a pet. The way gameplay with this class would go is that it'd be kinda meh until level 5--then you'd be the strongest character in the party by far. That would then taper off as enemies caught up with your dragon, though you're still controlling 2 full-fledged independent characters--til you had another massive surge in power at level 10 that would largely carry through until max level--with another (frankly obscene) power surge at level 20.