>>19294296They were a bit vague if the worst of what he pulled happened in X, so him joining made some sense. By worse, I mean the whole "Push Puru II as a weapon all the way and get her clones killed". He does push Puru II, but at the end of the day, regular Puru was still alive and they stop him before he goes too far.
What T does with him is way stranger, one of the weirdest things I've seen between games.