It is bad for the health of ranked. I can play every role but every role is designed to do different things in the game. Why force me to play something I wasn't planning on playing? My whole team ends up tilted because I got autofilled into a role I don't main.
why make us pick roles if we are not guaranteed to get them, that just throws out the entire balance of ranked. It is like every 5 games you play in sc2, 1 of them you have to play another race other than your main. Your mmr would be fucked and that is in a 1v1 game.