someone like that doesn't just change overnight.
when you're that good at cs (at NiKo's kind of peak), you'll get frustrated when your teammates suck ass. that's where pros like niko fail if they get power, they'll surround themselves with people they think are "good enough" to play with them, usually super-star talents or people that were super-stars (hence the signing of cold and kjaerbye instead of actually good players). Plus if you go by his stratbook, he doesn't change, it's just the same shit over and over while expecting a different result. He wasn't meant to have that power in FaZe to begin with, but guess what, he weaselled his way into it.
NiKo will probably do the same shit ruining teams for a few more years and then eventually transition back to player one he's wasted most of his peak. He's shox 2.0.
It's clear from your justification of kicking amanek that you don't understand how roles work or what amanek actually does for G2. Even though amanek will probably be kicked if they sign niko, the right person to remove would actually be jackzz. Even though he's an insane entry, NiKo is better suited to taking jackzz spots/ roles than those of amanek. If jackzz goes, G2 still have that supportive element while upgrading a player.