What are the consequences of denying Quickened Eldritch Blasts?

Question

A follow up to Can you use Quickened Spell to cast cantrips? (and asked in the spirit of this question and this question), a L18 Sorcerer/L2 Warlock has 18 Sorcery points, and "recovers" 2 (so to speak) at every short rest (due to Warlock slots). This means that, for 9 rounds, this character can pump out 8d10+8d6+40 force damage vs AC every turn (including Hex), and push the target up to 80 feet (with Repelling Blast; a minor point, but worth mentioning). And they've yet to use any of their spell slots: if the character converted all their slots to SP, they could do this for 35 more rounds (unless my math is off, L18 Sorcerer/L2 Warlock = 70 SP in slots) + 1/round per short rest (due to Warlock slots).

So, a few thoughts:

1. Given that AC is the most reliable defence to target, and force damage is rarely resisted, this is extremely dependable—there are very few (if any) encounters where this strategy isn't viable.
2. The damage is better (more DPT) than casting Disintegrate 9 times in a fight—all while "using" only nine L2-worth of slots. In fact, it's better to convert an L6 slot to SP (instead of casting Disintegrate, for example), and pull this off over three turns—you'd get 12d10+12d6+60 extra damage vs AC, compared to Disintegrate's 10d6+40 vs Dex. And I'm not even subtracting the opportunity cost of the EB that wasn't cast. Comparing the use of 6 SP over 3 turns (2 EB per turn over 3 turns, vs 1 Disintegrate + 2 EB also over 3 turns; click the Summary tab for easier comparison), you get about 336 vs 187 average dmg.
3. At the end of the fight, the PC can convert several low-level slots to recover a bunch of SP, ready to repeat this in the next one.
4. And, the main thought: this breaks the attack economy, given that the weapon-attack equivalent (Haste), has a built-in restriction that prevents precisely this outcome (the extra Action granted can only be used for a single weapon attack). So, a Fighter would get, at most, an extra 1d12 + 5 + 3 plus... nothing that comes close to 4d10+4d6+20.

In short, unless I'm missing something, this is way more single target damage than any other class/ability combination, from up to 120 feet away (in an open space, you could even stay away of 99% of threats—and push them back 80 feet if they try to close in!), and way more damage than any single-target spell. Which means that, unless you're fighting multiple targets (and absolutely need some CC/AoE, or need to escape), there's no better use of SP, spell slots, or (bonus) Actions: spamming EB + Quickened EB is simply the best strategy to ensure victory asap.

So, what's the impact of a house rule denying more than one Quickened Eldritch Blast ray? Please refer only to your personal experience (or some suitably-backed analysis, according to good subjective criteria), and whether either scenario would break something I'm not seeing.

Answer 1

I'll try to answer your concerns one at a time, then give you my experience with a similar issue.

1. Yep... Eldritch Blast is extremely potent and has almost no downsides. It's primary purpose is to give the Warlock a best-of-breed damage cantrip, and it does that very well. Your assessment is spot on. I think the only thing you might be glossing over is the fact that to get your damage expression, you'll need to hit 8 attacks in a row. Assuming you're min-maxed, your plus to hit will be +11, whereas the average AC you'll be facing is in the low 20s. Although your max damage expression is 8d10+8d6+40 damage, your statistical average is probably closer to 4d10+4d6+20. Still very potent, but not quite as astronomical.

2. In terms of pure damage, you are correct that this is probably more optimal than Disintegrate (although again, you'll need to take the statistics of attacking vs AC versus making a Dex save against).

3. This is a standard Sorcerer ability that allows the Sorcerers to cast more spells. In a DMG Approved, 8-encounters-per-rest adventure this is necessary to keep them competitive. In a real-life, 2-or-3-encounters-per-rest adventure, this makes them very powerful. If you followed the DMG to the letter then your Sorcerer will likely have to ration out this Eldritch Blast hailstorm, which would bring the power level down a bit.

4. Yes, your strategy is superior to Haste insofar as dealing damage. You don't gain the additional speed but at level 20 speed is meaningless anyway. However, Haste also gives you a +2 to AC and advantage on Dex saving throws, so the true winner depends on what encounter you're facing at that time.

Now, in my experience, this is what I've seen.

Level 20 spellcasters are absolutely insanely powerful

Any spellcaster that makes it to level 20 is essentially a demigod. Comparisons between abilities at that level is very difficult, because they're all so absurdly capable.

In this case, your Sorcerer is extremely good at dealing force damage to one creature at a time for about 9 turns per day (more if you sacrifice your spell slots). However, at this level the other casters in your party can summon things like Tsunami, Meteor Swarm, and Storm of Vengeance that, due to their AOE attacks and the fact that level 20 encounters are usually brimming with minion-type characters, can do far more damage in a single round than your Sorcerer can output all day. There are also status-effect spells like Imprisonment, True Polymorph and Wish that can completely end an encounter before it even begins. So while your Sorcerer is good at damage, they by no means outclass other casters in the ability to end encounters quickly.

This leads me to my second observation, which is

Martial characters at level 20 are complete jokes compared to spellcasters, and you can't even begin to compare them to spellcasters

In your examples you're comparing your Sorcerer to a Fighter for additional damage gained by Haste. A level 20 Fighter is so far behind a level 20 Sorcerer that it isn't even funny. By level 20, the Fighter is completely outclassed in all areas of combat. It really isn't even close. By level 20, the Fighter's only job is to stand around and try not to die while the casters finish the encounter. If you try to find parity between casters and martial characters (especially at high levels), you're just asking for disappointment.

Finally, to answer your question directly, in my experience (for something similar but not exactly the same, basically house-ruling away certain spellcasting abilities at high-level play):

If you house rule this away, your Sorcerer will probably be mildly upset at you for a few games and then forget about it

It sounds glib, but really this houserule won't affect much other than the Sorcerer's damage output per round. In our case, the affected player was upset at first, but quickly realized they were still incredibly potent in combat. They never quite achieved the level of power they envisioned, but they didn't take long to adapt to the new restrictions.

The reason I don't believe that this will be a big deal in your game is that there is nothing mechanically that this build gives you other than massive amounts of damage. Anything the party could do with this build they can do without it. Mechanically your end-game encounters will take longer (your Sorcerer is now doing about 50% of the theoretical damage they would have before), but at level 20 the combat encounters are extremely variable and swingy. There are simply too many encounter-ending abilities on both sides that it probably won't matter much.

As long as your Sorcerer hasn't spent the last 20 levels crafting this character to have this ability and you're taking it away at the last minute (which would be pretty mean), then aside from hurt feelings there's going to be almost no difference (at least in my experience).

Answer 2

There is no problem with this, only happens 9 rounds per day.

Quite similar to the question about archdruids, and the answer is the same:

High level characters are supposed to be strong.

To go deeper into detail, why this is not as bad as it looks:

• You lose half of your damage for a round, if you fail the Concentration check, as you have to restart your Hex. After the enemy sees what you can do, they will focus all their attacks on you
• If you are stunned, incapacitated or paralyzed, you do nothing. When you are on high level, lots of enemies can do that
• If the enemy poisons, restrains or blinds you, you get disadvantage on the attack rolls. Enemies do that even on the middle levels
• Any debilitating effect has a lesser impact on a caster using Fireball for example, it still does half damage on a successful save.

So while you are unusually powerful, a smart DM can deal with it without any problems.

Answer 3

The impact would be that your player is likely to kill his character off.

This player has clearly built this character to be specialized at one particular function, keeping something pinned down and away from the group.

The consequence of removing the capability that the player is exploiting legally is that you're removing their fine tuning of a level 20 character.

Ultimately, any class can play around multiclassing for purely absurd results. The problems start to crop up with high level characters. Like a druid 17/pally 3 combo which allows you to shapechange into a Hydra and smite every single time you make a melee attack (as just a base hydra before you start regenerating heads that's potentially 5 attacks with 5 smites. That's {[5d10 + 25] + [25d8]} per round if each attack hits. And that's just a CR 8 hydra. Imagine a Marilith with it's seven attacks.) Since druids have full caster progression, that's a lot of spell slots that can be chewed up to deal tons of smiting damage.

Subjective opinion below:

If you're just looking for a hard counter to this particular tactic, consider giving an enemy boss boots with an immovable rod sewn into the heel so that it can't be shoved around for the battle (rod engages when enemy has weight on the button, disengages when he lifts foot).

Alternately, you could not allow for multi-classing, which would remove the benefits the player is gaining from Eldritch blast which are Warlock specific.

You need to decide what is going to be legal, and what isn't. If player's aren't able to capitalize on their multiclassing abilities, they need to be informed before they create the character. Their expectations, and your own, need to be something that is laid out in advance so that there isn't any bad blood later.