I like how XY didn't need to resort to depowering Pikachu (start of Hoenn, or Zekrom in Unova) or resetting Ash's experience just to give him a challenge, same as Sinnoh. Sinnoh and Kalos asked Ash to up his game (it helped a lot that Paul stood on equal footing for Ash instead of being a newbie trainer, which combined with Zekrom nullifying Pikachu's electric techniques is where BW stumbled with Trip), and he did. Alola sidestepped this by not being the conventional walking the earth journey.