There should absolutely be an option to only queue with teammates and opponents who are also solo queueing. Whether its unrated or comp, you should have an option to not play against a five stack with a four stack that you're not part of.

If you don't mind filling into a 4 stack or pair of duos, fine. But I'm sure a lot of people do mind it, and they shouldn't have to waste time with teammates that won't talk to them against a full, coordinated team.