I understand the point of view that if you get into a to4 you should get to enjoy the advantage, and that solos should be punished and learn to party up.
But I fundamentally disagree with it on several levels.
First, I have no qualms at all about completely removing that advantage if possible. If I can find 4 solo players who play well enough to challenge a to4 and make the match 50/50, I will do it EVERY. TIME. It's not like a to4 is going to be playing these 4 solo players and thinking, "Whoah, this sucks because they are playing in such a weird and different way than an equally skilled to4 would play, this is so different and not fun"
The contract matchmaking has with our players is to give as close to 50/50 as we can. We're not going to give you easier matches because you're in a to4. If I had unlimited to4s to matchmake you with, I would still give you a to4 of exactly your same skill and call it good.
The problem is, at the very top, unless 4 Pro players happen to be searching solo at exactly the same time, it will be impossible to find a group of 4 players who can go 50/50 with a Champ to4. So it will be almost impossible for a player to get to the top of Champ playing completely solo, and the very top teams will go higher than 50/50, and that's also fine. So as far as the top of the leaderboard goes, it will still be exclusively to4s, except for the occasional Pro who can sometimes carry even at that level.
Second, there's no reason for me to make a to4 wait an extra 20 minutes until we find another to4 of their own skill before they can play, when I know I have 4 solo players who will give them almost exactly the same experience. Likewise for 4 random solo players near the top. If the gameplay experience is the same, I have no qualms about making the match.
Players are happier and stay engaged in the game more if 1) they find a match faster and 2) matches aren't unfair. The only way to do this across the board fairly is to aim for 50/50.
And as to your question about comms, yes, we still have millions of data points showing players on comms losing to randos. That skill gap is just as quantifiable.
I've been matching larger teams for almost 15 years now, and haven't seen anything to change my opinion on this.