At the moment, it seems the matchmaking only averages the competitive rank of the whole team, and that's all. I think there should be a limit (per example, bronze players can only play with bronze, silver and gold), etc... And also a minimum lvl required (or match low levels with low levels). I know this can lead to longer queues, but I don't think this kind of matches are fun:
Diamond player with a lvl 1 and 3. The enemy team looks almost the same. And we had a leaver (there are a lot of leavers). How is it fair to team up a lvl 1 with a Diamond player? They don't even know what's an objective.