Even for a person, if a group is just chain queuing, a lot of the games will be stomps. And while its kinda fun to stomp - you don’t really get to fully play the game since your enemies are just so slow and unprepared.
The contrast is that a good team v team wsg is super draining. Very few groups will want to keep doing them back to back.
MMR fixes that by letting people get good games without having to organize with 9 or 19 other. So people can play as much or as little as they want without impacting a whole team.