Again, this wouldn't be a problem if Kalos didn't shaft basically every other character so it could center everything around Ash and (later on) his 'very special' Greninja, or if it gave him something to achieve, beyond placing second against a trainer he's lost to thrice. He was built up as this incredibly powerful trainer, one who could fight toe-to-toe against a Champion's ace Pokémon. Heck, they even included a scene where a trainer broke down in despair due to not being able to make it, which ended with Ash confidently assuring him that he'd win it all for the ones who weren't good enough.
Kalos, in the end, was empty hype. It felt 'cool' and it looked great. However, the series spent most of its time building up to a huge victory for Ash, which...never happened. It wasn't 'just a league loss', because the only thing Ash had going for him this series was 'LOOK AT HOW STRONG AND COOL HE IS'. If you don't do anything with it aside from a villain plot (and like, Ash saves the world on a weekly basis so it doesn't even feel impressive), it all falls apart. There's no point in building a season that spends literal years showing Ash as this nigh-unbeatable trainer if you don't really do anything with it.
Anyway, rant over.