People still go back and play FFVII, VIII and IX. I have. They not only hold up, they are better games than most RPGs today and certainly better games than FFXV.
Better story, better characters, better and more deep battle mechanics (materia and GF systems better than anything in ffxv), more varied locations, more mini games, more *meaningful* side quests rather than time padding MMO nonsense, more people to talk to, more world building.
These aren't rose tinted glasses. The games were just far better made. More content, more meaningful content and better content. Better and more coherent style and story telling. They are holistically good games.
Nonsense. People disliked it for perfectly valid reasons. Poor story telling, unfinished game, shallow combat, piecemeal DLC side stories for the party members, MMO fetch/rat killing side quests, empty and boring open world, having to watch a sold separately movie to actually get background and context to the game etc etc
Trying to hand wave all these perfectly valid criticisms of FFXV as "people don't like it because it is different" is very intellectually dishonest.
FFXV is a very poor RPG. And, quite opposite to your argument, if you took the FF name away from it I'm fairly certain it would have been utterly trashed by everyone. Imagine some no-name RPG released a completely unfinished game, with an awfully told story, gated all the personal stories of the party members behind DLC, completely empty and dead open world and filled it with time padding MMO fetch quests and had a brain-dead shallow combat system. Nobody would give it the pass FFXV got because it was FF and had been in development hell for like 10 years so people were just happy to see it exist. It would have, rightfully, gotten 6-7/10 across the board which is what it deserves.
It absolutely does not stand up to the legacy of FF outside of flashy visuals. Anything else, of substance or depth, is mediocre at best. Mediocre open world. Mediocre story told awfully. Mediocre battle system. Mediocre side quests. Released incomplete and charging for character side stories.
I played Xenoblade chronicles 2 after FFXV, and while I was not a fan of the art style or the fan service the actual game itself was a masterpiece especially in comparison to the dumpster fire that was FFXV. It had an amazing story, an interesting world, deep and fun battle system, great characters and best of all the DLC was basically an entire other game and it didn't feel like I was being sold bits of the game I already paid for.
It had a worse art style and graphics than FFXV, but everything outside of visuals puts FFXV to absolute shame.