While I get that adherence to the established lore is definitely preferred, I'm not sure if that really prevents Larian from telling a compelling story with their modified version.
I do wish there was a little more acknowledgement of how atypical this is for illithids, rather than the Emperor sometimes acting like he speaks as a normal example of their kind. And I'd like a bit more justification than his "strong personality" -- did it have to do with being rescued? The attempted treatments he was given? Precautions taken before transformation? He was a renowned adventurer, after all -- if he tells me that some previous magical protections, skills, etc. that he'd developed contributed to this, I don't think I'd be too bothered by that; especially if teaching this to the player was part of how he ensured that they would also "survive" the transformation.
Mainly, I just wanted to see a more interesting arc or storyline from interacting with this character, even if it deviates from the D&D lore.
I agree that Larian shouldn’t be strictly beholden to lore. DnD has had many changes to lore over the years, and if they’re moving in the direction of more nuanced character development, I think that’s great. I’ve heard there are other renegade illithids found in some forgotten realms stories, but I’m not familiar enough with the books and campaigns to verify that.
The “strong personality” wasn’t an explanation as to why he’s different. It was The Emperor lying to Gortash and not telling him that
Ansur saved him from the Elderbrain.
As for the reasons of why he’s different, I think a lot of times when people are analyzing a story or character they assume every minute detail must have an explanation, when unless it’s story breaking, it’s not that important. He’s different because he’s different, and who he was before turning seems to have had something to do with that, but the exact details don’t really matter. Likely, as far as story telling, having The Emperor have this legendary past is more satisfying as to why he’s different than him being just some adventurer. Omeluum is also different and we’re short on details for him as well.
Omeluum talks about breaking free from his colony through arcane magic,
but the minutia of how he did that doesn’t matter. He broke free, and he’s another example that not all illithids are the same.
