They could tighten up matchmaking tomorrow, to the point where no one was in a match with more than a 5% skill delta. And it would make absolutely no difference to your matches at all. Because as soon as the one shot wonders realized what had happened they would all switch over to a secondary and suddenly your legit "tight" match would have masters and predators in it. Even if your legit rank is bronze.
Everybody thinks this game has a cheating problem. And it does. But it also has a smurfing problem, and the real kick in the teeth is that cheating may be hard or even impossible to stop, but smurfing could be ended tomorrow with three lines of code. The developer chooses not to end it. They are consciously, deliberately choosing to allow players to indulge their worst natures, to showcase the death of sportsmanship, to encourage it... all at the expense of normal, everyday players. And then they wonder why there are almost none of those left.