In my 769 games, the Umayyads are always smashed to bits, regardless of whether they manage to form Hispania. I even play with Sunset Invasion on(Umayyads are usually long gone before they arrive), and the Catholics do fine after the initial wave dies down because the Aztecs can't govern for shit.
Playing as a Romuvan empire in my current game, I've been raiding the Catholics for centuries, three consecutive crusades for Saxony against me have failed, at one point they lost both Spain and the British isles to the Aztecs(before 900, and they also reformed), Italy has been ruled by orthodox christians for around 200 years, a Catholic hasn't ruled over Rome for almost 300 years, and their moral authority has dropped to single digits multiple times, but they've managed to hold on.
That said, the current year is 1139, and things have recently taken a turn for the worse for them. Within the past century they lost Spain (again), this time to a Berber Muslim who managed to form the empire of Maghreb beforehand, and the Italian Orthodox ruler recently won a claim for the kingdoms of Austrasia, Germany, and Castille. If it weren't for my intervention, they would at least have converted all of Scandinavia, but I've made converting the Norse my pet project.
Uhh, I kinda rambled there, but my point is I've played a lot of 769 games and I've never seen the Catholics completely collapse. I might see it this game, but from what I can tell, that's mostly because I'm antagonizing them. I think this is mostly a YMMV type thing, as many things are in this game.
At least the Byzzies are doing fine this game.