I feel the OP post shows a little ignorance in the system as a whole. ATMtheWookie wrote a good post. The last thing in the world we want to do is to go back to GP matchmaking. 1. Winners win, losers lose. That's not the case now with even-ish win/loss rates. 2. Players will min-max their rosters, which is the last thing we want to deal with in a collection game. It would also mean starting new accounts maybe more viable to keep a leaned out the roster. 3. GP is a poor measurement for actual GAC power.
As for matchmaking with GLs.....that's never going to happen. You're basically asking for f2p match ups and p2w match ups. CG are never going to do that, you're requesting them to favour f2p over p2w.
I also think there are very few players deliberately losing to get easy match ups. Those that are, probably aren't very smart (from my perspective anyway).
I'm repeating myself here but.........................there will be few I think, that will disagree that the larger accounts in the lower leagues is very wrong. I like you, feel that this does need to be dealt with. Something like "Players' accounts a certain percentage over the division's average are pooled together into their own groups". Would be far better, and would deal with the problem much better than total GP match making.