>>47946201gamefreak has been absolute ass at optimization since the beginning always needing interference. hence the whole "gen 2 was compressed so much they could add kanto" and iirc gen 1 got just enough space saved to toss in mew (i dont know if that one is true i haven't heard the story in years).
then there's gen 4 being scuffed.
the entire 3DS era cause they were using models too quality on a 240p screen so caused massive lag so they had to cut out all the battle modes like triple or rotation due to their models causing too much lag.
and then swsh being ass being sub 10fps with online enabled, slowdowns in other times etc etc etc you get the point.
gf has hardly ever put out an optimized game in their lifetime