In a way, it is partially PSG's fault because he has become too special since he became the highest-paid player in the world. Currently, he is turning into an immature person, so he needs some motivation to change his ways. It is definitely necessary for Mbappe to check his ego. In a team with Messi and Neymar, he would be able to learn and gain a lot.
I don't think that the major problem with Kylian Mbappe performance right now is about him being the highest paid player, rather might be that his mind isn't with PSG anymore since Real Madrid indicated interest about signing him last transfer window and a possible deal completion next January window transfer open. Mbappe really love to see himself play for real Madrid right from time and knowingly that a deal is set for him to play for Madrid could make him this lazy and wouldn't like to put much effort in his games at PSG.