Anyone else disappointed in the Crimson Monastery storyline?

Hi all, I'm the DM for my group, and I'm considering heavily rewriting the Crimson Monastery chapter. It just feels like they went "spooky religious horror" without much consideration for what would make sense for the Fallen involved.

Marius is a paladin who got corrupted through deception, so why would he just be terrorizing random peasants instead of still trying to do good and taking more and more "the end justifies the means" extremes, or punishing ever smaller infractions? Why are his main followers (incl. his former squire) moustache-twirling, sadistic assholes?

Also, why are they burning people? They're vampires, seems like a waste of good blood when they could just "purify them" by draining them.