The matchmaking system is full of shit.

I've seen way, way worse?

It depends on what the win rates are

This seems stable. Not sure what's the problem.

That level 30 is always a wild card. Could be better could be worse. You probably wouldn't be complaining if you knew that level 30 was a platinum 2 smurf.

And there have been matches with even more disparity. Like when you get a team ranging from Platinum 4 to Platinum 2 going up against a team that has 4 Bronze tier players and 1 gold 5 player. Those matches are far worse.