Normal person here:
XY has a cool setting and somewhat of a cool dex if you're a boomer like me, but megas are annoying and it's a bit retarded that you get a really strong one for free early on. If you don't drop it, it will carry you for the whole game, you do not need any other pokémon. The post game is bad.
ORAS is a bad remake with really bad aesthetics. They deleted the postgame. However, the Deoxys thing is really, really cool. Not worth a playthrough for it, though.
Sun and Moon can be ignored because USUM is the full game. USUM is borderline chemical torture by the FBI, the characters are very, very annoying (no, not like green/blue annoying, REALLY annoying), especially your "rival" hau and lillie, both awful characters with poor characterization. It's easier than XY and the game handholds your ass for the whole ride. Arguably has a cool boss but it's not worth the hours to see it.
IMO I'd skip the 3DS games, they're generally bad, especially if you're coming from Legends. You could give SWSH a try.
