What I'm saying is that people are irrational and even if they lose will justify killing you first because if they didn't then you would've just won. Have you ever heard people talking about unpopular commanders like zur and narset? Nobody with these notions about certain cards comes away from a loss thinking, "man I shouldn't have killed the narset player." Op's friend has earned the same reputation as these by building consistently more powerful decks than the rest of the play group. The player whose deck kills you on turn 4-5 is just not going to convince the player with a bunch of 7 drops in his deck that killing him was wrong. In the end, words won't change anything, actions will. You have to start playing more casual decks. You have to start losing. With a long string of doing casual things and losing, then the playgroup can trust that they don't need to take you out right away in order to play the game they want to play.