I think the Champions of Filth/Oath of Pestilence would be better if they were more religious.

Their philosophy is that disease makes life stronger, and it's their duty to spread it without regard for law or morality. Which is a fine motive for a cult of strength.

But the Player's Guide depicts them as paladins, which makes me think they have some great potential as a religious cult.

Instead of understanding that the Weeping Pox is a morally neutral force of nature, what if they saw it as divine judgement? They would believe it only kills those who "deserve" it, and the fact most people don't survive is just proof of the inherent evil of mankind, and that they are the blessed few.

I think that allows for more nuance based on each knight's personal views of morality, and who they decide to infect.