Summarizing

I figured for this one, I'd just write why I think Paul qualifies as a Messiah. The Fremen Messiah is called the Mahdi, which means he will lead them to paradise. The Lisan al-Gaib, another name for the Messiah kind of, will share the Fremen's dearest dream, which I assume must be followed through on, the greening of Arrakis. Paul and his mother fulfilled various other necessities, such as knowing certain prayers and aspects of life on Arrakis. What I think is necessary is to divorce the concept of Messiah from religion altogether. The Fremen Messiah is not the son of god or a god himself, but instead just the first guy to come along and deliver them from oppression and Paul is that guy.

As to the question of whether the whole religion is false because of Bene Gesserit contamination, I think this is overlooking the fact that the Fremen had a separate religion when they arrived, and that the Bene Gesserit words are simply additions. Similarly, just because Paul goes about being the savior systematically doesn't mean he's manufactured as well.