tbh i feel like the real reason illumi turned out the way that he did (controlling, putting his family needs above his own, etc.) is mostly because he was the firstborn child in what was going to be a dumpster fire. like am i approving of his actions? hell no, but when you think about it... how else was he supposed to turn out?
cause he's their first kid so all of their attention is really on him until milluki is born and im pretty sure theyre around 5 years apart so he grew up with that for five years. and after they had milluki... yeah lets be honest for a second they probably realized he kinda wasn't worth training all that much and focused more on illumi which... YEAH PROBABLY NOT GOOD
and the reason that this is so bad is because he probably didn't interact with any kids when he was younger like at all. most likely because his parents told him not to and yeah, he (probably) listened. killua didnt of course as we see his interactions with canary but he didnt listen and thats probably because he saw how illumi turned out and was like 'oh that does NOT look good'
while illumi on the other hand really didnt have anyone to compare it with, to see like 'oh this is probably not a good thing' because that was his normal. and of course it's also killua's 'normal' but the difference is that killua was able to look at that and realize that that was not normal. illumi couldnt do that, being homeschooled and all he didnt grow up around people his age and yeah that made him kinda... eccentric in a way but still.
if you were put into a room with no memories and someone started telling you what to do obviously you're going to listen to them, especially when they're the ones taking care of you. youre gonna listen to them no matter what because in your mind they most likely care for you because you're still alive and such. however over time they might start molding you into something else.
now imagine that same scenario getting put into a room with no memories and such except there are other people in the room with you, one of them has obviously been there the longest but that doesnt matter because there are other people and you realize 'hey this is kinda fucked up' and you manage to leave.
thats basically how i picture illumi vs. killua in terms of what they realized growing up, of course personality is definitely a big factor but also who and what they grew up with helps.
like i truly believe that if killua was born first he'd be just as fucked up if not more fucked up than illumi (mostly because theyd HYPERfocus on him and stuff because they believe he's 'the strongest' or whatever)
yeah anyways thank for coming to my tedtalk ig