5-man teams should only go up against 5-man teams, even in normal games.

Communication is a huge part of league, and it's undeniable that a team with better communication has a serious advantage against one that doesn't. Queues, including normal games, all strive to put teams of relatively equal skill against each other. Putting a single duo and three solo queue players against a 5-man is not a balanced match. 5-mans in ranked have their own queues, and there's a reason for that. Playing against a 5-man as a solo player feels absolutely terrible.