When you get over 550Mgp, there aren't many "tougher matchups" that you can get if you win consistently. So "Win 2, get a tough matchup" doesn't work well there.
Likewise when you're in a very low-end guild. (What is a low-end guild these days? 80Mgp?) Only at that end it's hard to give you a cupcake.
But they do try to do that. Obviously there are some other factors or you wouldn't see guilds with 11 win streaks, but it's neither strongly GP based the way some people like (or fear) nor is it entirely skill-rating based the way GAC operates.