Assassin would make sense, under similar logic to the justification for the removal of the Assassin class in 2e - anyone who commits political murder and/or murder for higher is an assassin, so having it be a subclass is a bit unusual. More importantly, they’ve struggled to come up with a satisfying version of the Assassinate feature. Players want such a feature to significantly increase damage, but the designers don’t one one subclass to have significantly higher damage output than the others (to their credit, I think). So, rather than continue to struggle to crack that nut, cut the subclass and replace it with a psychic subclass, since that’s something there’s a certain demand for anyway.
EDIT: Presumably Psi Knight replaced Brawler.