I hope it's the new standard, though I'd like it if a future generation or game touched on the minor league. They mentioned it several times yet you never meet anyone associated with the minor league nor get an idea of what it's like. Imagine if you had to battle your way through the minors in order to fight the major league trainers? With the major league trainers being juiced up endgame tier like the Kanto gyms in the Johto games
They're certainly a step up from the snoozefest that was Kalos' gyms for sure. Actual upbeat music (though Gens IV - V remain supreme on this in my opinion) helps a lot. That said, I find it so odd that there's always people in the stadiums no matter what. Do they just sit there 24/7 or something? And while the difficulty is what I'd expect from gyms, I did like Raihan's gym match a lot along with Kabu's.
The fact that they have jobs/hobbies outside of their Gym Leader status (photographer/artist, sports enthusiast, Mega Evolution successor, gardener, inventor, model, fortune teller, Pokémon Village protector) makes me think that, like lots of XY, they didn’t have time to fully expand on it.There's also the fact that the Gym Leaders actually do something other than stay in their Gyms, even if the Stow-on-Side and Circhester Stadium folks are pretty reclusive thanks to them being version exclusives. It's a directon taken in Generation V that they've been doing since (except in VI for some reason--the Kalos Gym Leaders are just there.)
Though it would've been pretty neat to see the stadiums get increasingly full the further you go. As popular as Milo is, he must have to fight hundreds of battles every season, and it wouldn't be the sort of thing to fill up a stadium.
I don't see anything wrong with Rehan's character. The only problem with him I see is that he's supposed to be a weather based trainer but the AI is too dumb to make effective use of that mechanic