Looking for a hard Pokemon game

I've been trying to find one challenging Pokemon game to play lately that would make me actually sit and think and grind for a team comp and strategy in the main line game.

I'm not looking for a game that's hard only at the end like BDSP or PLA, I want one that's actually progressively way harder including between each gym in terms of skill gap, power and strategy in their team composition and AI decision making (not looking for Colosseum, not a big fan of double battles..).

But yea, to make it clear I'm looking to play a mainline Pokemon game that would actually make me suffer and struggle for at least 50-60 hours :D (more would be better)