>>38776814PokeMMO does it by giving decent IVs to trainers and increasing them as the story progresses,giving each trainer a varied team with good moves, and having an AI that's decent enough to follow basic strategies/switch for better matchups and shit. They also stop you from overleveling by having a cap based on the amount of badges you have.
All this creates a more enjoyable experience since you sometimes have to come up with a strategy to beat a certain AI that's giving you trouble. Gamefreak won't do any of this because that would mean striving away from their old ass stale formula.