You bastards should actually try to convert a Fissoan or two, so I can join in on this conversation.
That's just another symptom.
And I'm not just dissing SA, or another other religion, for the fun of dissing. I've involved myself heavily in the religion game for as long as I can remember. I've founded a religion, I've helped others found religions, and I joined a number of religions of various ages, of which I often rose to elder ranks. Most of my characters have been priests for most of their careers. Guillaume, Machiavel, and Louis-Joseph, notably. And that's not counting the number of religions I've interacted with from the outside.
Religions are made to be inconsequential. It's built-in, inherent to their game mechanics. And players, in general, understand this. Some try to make religions matter despite their inherent flaws, but almost invariably fail. Some manage to be more meaningful than others, but very few manage to actually be a driver of change, instead of just a flavor coating on things that would have been done anyways for other reasons.
The argument that "make X (religion/realm/other) fun, and it will succeed" is false. But how do you measure success of a religion, anyways? Number of temples? Number of peasant followers? Number of noble followers? Number of noble followers who would actually listen to their religious elders if tasked with something? Number of noble followers who promote the religion of their own initiatives?
The Cult of Bloodmoon is not a successful religion by any standards. It is not a young religion, it is by now quite old. And yet it has never really spread beyond a single realm, migrating with its core as events dictate. Controversy may have a role in it, but it can't be blamed for it either. The Blood Cult, who openly professed human sacrifice, had, at its peak, followers in 6 or 7 realms, and being the state religion of one and a major religion in a few. Your success is lesser than that of Torenism.