The issue here is not one of power, but of fairness. If the paladin were also not allowed Leadership, I think we could all agree the GM is within his rights to say, "I don't wish to define NPC relationships in my game that way." But if the paladin can have followers, the wizard should be able to.
I think DMs are within their rights to say any crazy thing they want about the rules of the game they're running. So even if he says "rocks fall, everyone dies," I think he's well within his rights.
But more directly to your point, it's only fair if you consider "equal treatment for each character" to be fair. I don't. I expect rogues to do better at traps, and they're going to get favoritism with regards to trappy things. I think that's fair. I expect half-elven diplomacy bards to be exceptionally good at social interactions, and I'm going to give them advantages that other low-charisma characters don't have. I think that's fair. And in the case here, the DM is essentially saying, "The charisma limitations of the Leadership feat need to be more extreme." That ruling will mean that certain characters get cut off, and certain ones don't. Frankly, I think that's fair -- it's not targeting this guy's character specifically, it's targeting anyone with low charisma. For all we know, there is another low-charisma character who will also never see the feat because of this. So it doesn't seem like a case where the DM is picking on this player. (But I haven't seen their interactions, so I can't really say.)
Your DM is an extremely generous DM just for letting you use your Int score for your Will saves. That alone is an incredible advantage for your PC.
Did you bother to argue with your DM that maybe this new feat is overpowered? I doubt it. So why are you going to post here in hopes of getting more ammo to use against him so you can pester him about his decision about the Leadership feat? That's obviously your intent.
Yeah, it's bad form and may piss off the DM if he catches wind of this thread.
My guess is that the DM was already feeling a bit overly generous with absurdly high Intelligence score, and then felt
doubly generous with the "use Int for Will saves" ruling. At this point, he probably feels there is some quid-pro-quo that needs to happen -- huge advantages have been conferred, and in exchange, he's probably expecting that no more advantages can be had, or at least whatever paltry negatives are left will be preserved. Now here comes the player asking for a feat that typically is only useful to high-charisma leaders. And the DM is thinking, "What the hell? This guy has so many advantages, and now he wants to use a charisma-driven feat, and I'm supposed ignore that charisma was supposed to be his dump stat? Gaaaah!"
I imagine that if the DM is pushed on this, he's going to compensate somehow. The initial advantages were probably given in good spirit. If he's brow-beaten into this one, he'll be resentful enough to undermine it somehow. That will frustrate the player when unforeseen issues arise. For example, the cohort is targeted almost immediately in battle, dies, and then the player has a penalty to his Leadership score. The player is like, "What? Are you deliberately trying to force my Leadership feat to suck?" And the DM will say, "Nope, them's the breaks."
In my experience, leadership has little to do with charisma.
Effective leadership is about self-belief and strength of character. It's about values and the example you set.
Which is... charisma.
