UGC is completely unproven as a high level 6s league (their biggest 6s match ever would be the equivalent of an Advanced pugscrim today), and has its own history of poor decisions and bad admins. It has existed for over a decade and was never once even close to competing with either ESEA or RGL 6s (and also lost its dominance in HL to RGL very quickly). Not to say it couldn't, but people seem to talk about it as if its some unjustly maligned and ignored league which would be perfect if we the players did all of the work of by migrating to it from RGL on our own.
Incidentally, I heard the same stuff when CEVO failed, that it was the players fault for not signing up, as if it's not the league's job to promote itself and incentivize signups—things CEVO ended up doing terribly or not at all.