I don't think this is an exploit. The reason why you are playing against teams with max level cards is simply you don't have enough teams in Modern and that is keeping everyone down. With more teams those accounts will be much higher and then you won't face them.

I play Wild myself and play many matches against teams equal to me. My win rate is very close to 50% and my account plays at Diamond. So the problem isn't the summoner issue, the problem is there's not enough matches creating the ratings inflation that is needed to offset the season reset.

And this proposal will actually end up speeding up the solution that the team has chosen to solve the problem you stated. If it passes, then they will be able to many more liquidity bots that will help at all levels to get teams to where they are expecting to be.