I’m not sure he’s super fussed about continuing to be Supreme Leader after he yeets his saber into the ocean. Rey does explicitly ask him earlier in the movie if he’s serving a new master, and he denies it.

Kylo’s plan since moment one of meeting Palpatine is to team up with Rey and kill him, which is amusingly basically what happens (besides the minor point that he joins Rey in the light rather than her joining him on the dark side).

The mind trick in TFA also rubs me the wrong way because it feels like another JJ Abrams nostalgia lift, rather than something the character would actually think to try.