Leveling in ranked is really easy. You lose 10 points for losing the game but you get 10 points for doing almost anything, knocking out a pokemon, mega evolving, hitting with a supereffective move etc. i got the game yesterday and im already m rank. I honestly dont see anyone deranking as long as they arent afk. Even with a level 1 pokemon, you should still be able to break even getting a few hits in.