I'm going to take my friend's hero on overwatch
That seems like a bad thing to do. Why are you going to take your friend's hero?
Because it's the only way to show him that I won't be his puppet anymore
Sometimes I get angry when people beat me in video games too. But if you steal from your friend, or if you cheat with your game, I don't think he would want to play with you anymore and may end your friendship. So I would just recommend that you play and practice so that you can win against him, and have a friendly time with your friend.
Hey its fine if my friend no longer enjoys the game because we can play something else.
It's wrong to steal a character from your friend in a game. This will make your friend see you as someone that cheats and your friend won't want to play anything else with you.