What are the possible balance implications for houseruling INT as Paladin's spellcasting ability and class features?

Question

Related (yet different): What is the source of a Paladin's spell-casting ability?

Related (strongly): What are the impacts of changing a Ranger's spellcasting ability? (I don't know if everything that's said about the Ranger is applicable to the Paladin)

My player wants to create (L1) an investigator-type paladin (of the Inquisition) and asked that Intelligence becomes the character's spell-casting ability and, if possible, also class features ability (e.g. Lay on Hands).

PHB states that:

Charisma is your spellcasting ability for your paladin spells, since their power derives from the strength of your convictions. You use your Charisma whenever a spell refers to your spellcasting ability. In addition, you use your Charisma modifier when setting the saving throw DC for a paladin spell you cast and when making an attack roll with one.

Since they are not asking for extra skills than the ones already provided by race, class & background, i.e. Paladins can pick from two Charisma skills (Intimidation, Persuasion) and one Intelligence skill (Religion) at character creation, I don't see any system-unbalancing issue in this approach.

Also, I suppose that Intelligence save proficiency should be awarded instead of Charisma on character creation.

To be clear, my issue is not the fluff of "the strength of convictions" (I'll probably trump it as "rigorous reasoning" ala Sherlock Holmes) but whether the PC becomes over/under -powered, compared to the normal Charisma-based option, over the short and long run.

In case it is relevant, it is a Human-only (for PCs) campaign, with options only from PHB (feats included) excluding multi-classing.

Answer 1

For a knowledge oriented Paladin, Intelligence makes sense. For a social oriented Paladin, Charisma makes sense. But do mind the Saving Throws.

I personally really like the idea. Here's why:

Exchanging one type of skills (Knowledge (Int) skill for Social (Cha) skill) honestly doesnt change much to the game, balance wise.

You end up with a knowledge based front-line fighter instead of a social based front-line fighter. Is that a big deal for your game ? This only changes what kind of situations the character is better at, out of combat (most of the time).

This change shouldn't affect any game seriously, as most game masters actually hope some of the characters in the group are good at social and/or knowledge skills, at least in my experience.

Where there is a real difference in my opinion is in the saving throws. And I only say that because I think the player is actually crippling his character a little bit. I think the biggest impact is you saying that if the Spellcasting ability is changed from Charisma to Intelligence, then the Saving Throws proficiencies are adjusted accordingly and changed from Charisma to Intelligence !

I say that because Charisma Saving Throw proficiency is a lot better than Intelligence Saving Throw profienciency. I don't feel like I even have to prove this point, as any experienced Players and GMs know that there are a lot more spells requiring a Charisma ST than spells requiring an Intelligence ST. Personally, if I asked my paladin to switch Charisma for Intelligence, then the saving throw proficiency would follow suit and I'd have to replace Cha for Int on that front too. I've never done that specifically, but I did do as your player is doing, in the past, and ask for a change that didn't make me stronger but still had an impact on the game except by making my toon better at an aspect of the game of my choice.

The paladin saving throw proficiencies are actually very good in a game where the GM exploits every possiblity and use all the 'dirty tricks' aka 'save or suck' spells. A lot of 'save or suck' spells depend on Wis, Cha or Con saving throws ... the paladin has 2 out of 3 on those proficiencies. I won't mention the damaging spells which are, mostly, Con and Dex based since in the context of this question it doesn't matter, since that remains a weakness of the paladin vs the figtrer (on the Con saving throws) or the rogue (Dex saving throws).

It's all about choice and I do feel like your player simply wants to play a paladin with a different flavor.

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This is totally subjective, but I would personally enable this player and maybe change the list of skills available to him at first level, replacing a Persuasion and/or Intimidation for Arcana and/or Nature. If the player is willing to use the Intelligence ability score, which has now replaced Charisma as the most popular dump stat in D&D, I personally say "go for it, this is not game breaking !".

Answer 2

Probably the character's power slightly decreases, since they multiclass Wizard instead of Sorcerer, but overall this is balanced

Int is currently the worst ability score in the game. It does almost nothing without class features that give it potency, and even those are few and far between. If you aren't a Wizard, you dump Int. Sometimes nobody is a Wizard and then maybe you don't dump Int on whoever's going to be the party Investigation dude, but often you can do just fine with no one with Int and pump Investigation checks you make with guidance and bardic inspiration and stuff. A single feat in Observant or Dungeon Delver will fix Intelligence's one use just as well as if not better than raising Int to 20, and is usually a cheaper long-term plan that assigning a good ability score to Int (though it does come at the cost of your primary rather than secondary abilities in the short term, so that can be rough).

Getting Int as the spellcasting statistic for a Paladin, then, would seem to be a very bad trade. Charisma, while innately basically the same as intelligence, is used for all manner of class features across all sorts of classes. If you were gonna multiclass, Cha is pretty much the best primary stat to have. This is especially true for a Paladin, who can get a lot out of dipping Warlock or Sorcerer (Paladin is pretty front-loaded as a class).

However, since you are actually using Int instead of Charisma for all purposes (Aura of Protection for example), this leaves the class approximately as good as normal, because they can just multiclass Wizard instead of the usual options. This is a bit weaker, because the Sorcerer's metamagic allows for better bonus action usages than the Wizard and the Warlock is no longer available, but it's not really that big of a deal-- you still get access to lots of bonus action spells if you are careful and Wizard is generally a somewhat better class outside of bonus action usage.

Note that an evocation wizard / Int paladin will add their Int modifier to the damage done by attacks made with smite spells, which is a significant improvement putting them ahead of the 'for free' Divine Smite option by a very small margin, generally. This is still not great because it eats your concentration, but it is at least less of a trap than for the typical paladin.