What are the impacts of allowing Rangers to cast Arcane spells?

Question

Background

Rangers have the spellcasting class feature. It allows the Ranger to cast a small number of spells from the Ranger spell list, which has a lot in common with the Druid spell list (much like the Paladin spell list has a lot in common with the Cleric spell list, although they aren't the same; Hunter's Mark for Rangers and the various Smite spells and Aura spells that Paladins get are examples of why they aren't literally just subsets of the Druid and Cleric spell lists).

The "Druid-y" feel of the Ranger spell list suits the more "nature-y" feel of the standard Ranger, such as those with the Hunter or Beastmaster archetypes from the PHB. But what about the archetypes from Xanathar's Guide to Everything? To my mind, they seem less "nature-y", and thus the "druid-y" spells they get don't seem to suit them as well. To clarify, it's not the "free" domain spells you get as per each of the archetypes from Xanathar's, but rather than default Ranger spell list, that I feel doesn't suit a less nature-y Ranger.

The character I have in mind is a Horizon Walker Ranger who is interested in threats from other planes, which to me says that such a character would be more interested in the Arcane than in nature and "Druid-y" spells. Why would such a Ranger who studies portals and other planes be able to cast Plant Growth, for example?

Question

I plan to ask my DM (if and when I make this character; they're a "backup" character idea at the moment should my current character die) if I could essentially choose from the Wizard spell list instead of the Ranger spell list, but otherwise have the same restrictions as per the Ranger table in the PHB (i.e. no cantrips, same number and level of spells, the same number and level of spells slots, can't use an arcane focus, etc). I would also leave the domain spells that you get for "free" as per the Horizon Walker archetype as-is.

Since I'll be learning Wizard spells, it might also make more sense to use INT as my spellcasting stat rather than WIS, but I've asked about that in a separate question (hence for this question, just assume I'm still using WIS).

My question is: What are the impacts of a Ranger using the Wizard spell list? How will the Ranger having access to, say, fireball affect balance? If this is overpowered, would restricting access to certain schools (a la Eldritch Knights and Arcane Tricksters) help to rebalance things?

Extra Details

I am considering multiclassing into Wizard, but decided that I didn't really want to do that. The DM isn't too keen on multiclassing, at least not in this game as, although he's a long time player, it's his first time DMing and he doesn't want to deal with multiclassing. This is why I want to have some backup to convince him of this idea of mine. He's already let someone play the UA "Revised Ranger", so it seems to be just multiclassing he doesn't like.

It isn't my intention to make my Ranger overpowered, or even any more powerful than the default Ranger. My core problem is that I don't think "nature-y" spells suit him, whereas arcane spells would suit him being interested in extraplanar threats. In particular, I personally was planning on taking mostly Alteration and Conjuration spells, which I feel would suit him better from a more flavourful, roleplay perspective, rather than just choosing the typical "powerful" spells like fireball, etc.

Answer 1

The DMG has a Workshop section for customizing your game, and one of the section is on "changing spell lists". It says (among other things) that:

Modifying a class's spell list usually has little effect on a character's power but can change the flavor of a class significantly.

So really, there should be no problems doing this from a power perspective and changing the flavor appears to be exactly what you're after.

You can find this section on page 287 of the DMG.

Answer 2

Others provided reasonable answers explaining that power-wise this is probably ok. So allow me to introduce a little bit different point of view.

Consider the wizards

If you have a wizard in your party, they might feel a little less unique. Of course, you would not be stepping on their high level spells or have nearly as many slots, but all those nifty utility spells? Suddenly the wizard is not needed for those. And that is their whole thing, they have the best spell list, not much else (I don't mean to say that's not enough for them), characterization-wise.

To lessen this (already minor, I admit) problem, you might want to consult your wizard (if you have, or will have, any) or even the other casters, and come up with spells/schools that don't overlap too much.

Answer 3

This will not make Rangers overpowered

Rangers are weak

Ranger is possibly the weakest class in combat, especially Beastmasters. The ones from the XGtE are a bit better, but they do not get many combat related features after Extra Attack, at least not on the level of Extra Attack 2 of Fighters, or Improved Divine Smite of Paladins.

Wizards get the best spells in the game

While there are some great spells Wizards cannot use, they have the best and largest selection of spells, many of which are not even usable by Sorcerers. This is understandable, they do not get many class features besides their spells.

For this reason giving Wizard spells to other classes can be overpowered.

Conclusion

The combination of the two above means that Rangers become stronger with this change, but not overpowered.

Answer 4

This is likely to notably weaken the ranger

Hunter's Mark is very nearly a class feature - it takes your concentration slot, gives you extra damage on multiple attacks per round (generally three, via any of a variety of feat options), and can last essentially all day with relatively limited investment of spell slots. Losing that spell by itself is a notable hit.

Many of the wizard's spells are about direct damage-dealing or other direct combat applications. Every action where you're throwing around a spell like that is an action where you're not, say, picking Attack. The ranger's basic attack (especially with Hunter's Mark added in, and reasonably chosen feats) is a significant amount of damage to give up - quite a lot more than the cantrips that the wizard would be using in his not-spell-slot turns.

Just for perspective, at eighth level, the Ranger still only has access to 2nd level spells (3rd-level comes online at 9th). One of the wizard 2nd level spell attacks is Scorching Ray, which generates three ranged spell attacks (int-based) for 2d6 fire damage each (6-36 total). Alternately, you have acid arrow, which generates one attack, doing a total of 6d4 damage on a hit or effectively 2d4 on a miss (6-24/2-8).

A light crossbow ranger of that level who's gotten the crossbow expert feat and who's currently maintaining hunter's quarry can generate three attacks per round of 2d6+(dexterity modifier) damage against their quarry target (dropping to two attacks per round on those turn when the quarry drops and they have to switch targets). With a dex of 18, that's 18-48 on the turns where they get all three hits, 12-32 on the turns where their bonus action is taken. Also, they're likely to be more accurate, for a variety of reasons. Then, next turn, without spending a spell slot, they can do it again.

Now, that's not the whole story. The wizard does have a decent number of non-damaging spells (hold person?), and 8th level is a particularly bad level of the matchup (after extra attack and two ASIs, before 3rd level spells). Still, "spends a highest-level spell slot for the turn and still can't keep up" is pretty bad, and it's not taking into account the possibilities of magical weapons, maxed dex (variant human), or the likely differences in attack roll.