If you ask people to play specific heroes, there's a good chance they'll play that hero poorly

I've seen too many people say "hey can you switch from Zarya we need a Rein", or "hey can you play soldier instead of Mcree" or "hey we need res can you play mercy instead of Lucio" inside of solo queue. If you force someone to play a hero they aren't comfortable with they won't play them as well as the character they are comfortable with.

I had an incredible Zarya on my team forced to switch to being a mediocre Rein only useful for the shield, probably cost us the game. You don't need the shield or Res or whatever that badly, maybe just roll with what people pick sometimes.

also a good way to get what you want is to ask "hey is anyone good at Winston? This genji is kicking my ass" and to leave it at that. Someone might take initiative. But to call people out to play someone specific usually goes poorly