Personality changes aren't meant to be prevented. The issue is if those changes make your dwarves unplayable. Are the personality changes actually causing mass unrecoverable depression spirals?
yes lol. My baron went from being one of the typically reliable starting 7 to a nervous wreck (never had a dwarf with that trait stay sane). It seems like once a dwarf gets a thought they can dwell on they're just as likely to get a personality change as before, and while a lot of the sillier dwellable thoughts have gone away basically any dwarf who experience miasma has prepatch levels of shifting. If it was just miasma from the corpses of invaders that'd be one thing, but miasma can be frustratingly common and difficult to prevent, especially if a dwarf gets retasked in the middle of eating and you get the "claimed food on ground" bug.
I get that you aren't supposed to be able to stop all !!FUN!! but going "oh crud, looks like the one dwarf it's literally impossible to replace saw something stinky and became completely useless" is just frustrating. Minor, everyday occurrences shouldn't completely shatter someone's psyche beyond all repair and doom them to inevitable insanity. Some sort of gradiation in miasma intensity so dwarves can tell the difference between "month old cheese rolls" and "my office is full of rotting crundles and my arms are going necrotic" would be nice. Maybe a special miasma thought that triggers if the dwarf also sees a corpse on the same day or something?
As it is though there doesn't functionally seem to be any difference in personality shift rates between this patch and the last, at least for me. It just feels like they've shifted from having a myriad of silly reasons to change their personalities to all remembering that one time urist mcchefface forgot to put away the dog tallow after mincing it.