That is all very true. I think he had a meltdown after the attacks on him for The Passion; God called him to make it, which meant that Satan was really lying in wait for him afterwards.
One of Mel Gibson’s problems, however, is that he doesn’t attend a regular Catholic church, but was in a Traditionalist “private chapel” situation. I don’t think they’re SSPX (it might be better if they were). Priests in these groups are usually legitimately ordained priests, but no bishop will actually incardinate them, although in many cases the bishop of the diocese permits them to have faculties as “visiting priests.
The problem is that this leaves their parishioners very isolated and in an uncertain situation, and also prevents them from getting the whole-hearted support of the Church when there is a problem.
SSPX priests are not validly ordained. That’s the whole point of bringing them back in the episcopal fold so that they can be validly ordained. It’s no different than if you or I were to declare ourselves a priest.