Pokemon has always been one of those franchises that just get consistently better with each iteration. Sure, there are some small aspects where an earlier game does better than a later game (ie, GSC having a visible day/night system while RSE didn't) but on the aggregate, they get better.
The games ultimately never stray too far from each other. Yes, RBY and XY have large mechanical changes between each other, but at their core, they're the same. To make a comparison, think of Call of Duty and Final Fantasy. CoD keeps to the same formula, only making improvements with each new release. FF utterly alters the fundamental mechanics from game to game. Both are making changes, but CoD’s changes just improve something you’re already familiar with, while FF’s changes bring about something totally unfamiliar. Pokemon is basically CoD in this analogy.
The only real changes (as in, a different take on the franchise, not just an improvement) have been in the forms of the story and Pokemon designs. The games have progressively focused more on telling a story beyond "become champion". As for the designs, they've definitely become more complex. I don't mean that in a "OVERDESIGNED PIECE OF SHIT LOL US 90S KIDS RIGHT xD" because I love a lot of new designs myself, just pointing out an objective statement.
I can understand why you might like RBY more than XY because you grew up with it, and hey, there's nothing wrong with that. Fuck whoever calls you a genwunner. But its silly to call it "objectively better" than XY, since gameplay-wise XY is nothing but improvements. You could make a case that XY's story is objectively worse than RBY's story, but that wouldn't make XY as a whole inferior to RBY, because they're both video games, and what ultimately makes or break a video game is the gameplay.
tl;dr XY are objectively the best Pokemon games, not HGSS
