So asking relative question about what's the hardest game and everything acceptable? I'm new here so feel free to edit my question if you want.
Asking what the hardest game in the genre wouldn't be acceptable for a few reasons, but the two main ones are that it's a game recommendation and is too subjective. Everyone is going to have a different idea of what's considered the hardest game in the genre, and some games one person considers really easy others will consider really hard. Due to this all answers will just be users posting their opinion, which isn't really what SE is meant for.
With that said, you'd be welcome to pop into our chat room and ask for users for opinions there. Another good option would be /r/shouldibuythisgame, which is subreddit for suggesting people games to play.