But the growth rate of LDS slowed down before the Mormons where with enough to take over the US.
Anyway if I'm not mistaken Skellagrim had claimed in a previous discussion that all that would be needed to prevent Christianity from taking over the empire would be to turn Constantine the Great into 'Constantine the failure', so everybody will go 'let's just not have a Christian emperor ever again'.
That would be me. That has to do with the Roman (and Pagan in general) views on religion. A good leader has divine sanction and therefore what he doing was pleasing to the gods or god, therefore the empire was prospering. If it stops working it's time to try something else, much like changing military tactics when your loosing.
That's why when Julian tried to refurbish oracles, the pagans weren't enthusiastic. Oracle at Delphi said it was closed and wouldn't work anymore, it wouldn't. Severids had a patron cult to Jupiter-something or other that was popular in 200 but abandoned in 250 when the dynasty was done.
Christianity if it worked was a good 'military tactic' under a successful Emperor. If it didn't work, it's an embarrassing failed attempt to placate the divine.
The faith short-circuited the tradition of seeing it as your responsibility to abandon a losing tactic because your personal salvation was at risk. That's what it was able to do for most of the 4th century and the Grandkids thought it was the new way or "be Christian or be Damned" was what it had always been.
EDIT: Please also don't ask me to sit through a long YouTube video produced by a frigging church to analyze your argument.
I think this is why these debates are fractious. One side, the ones skeptical of Christian exceptionalism are looking at and trying to understand history as it was, while many on the other side (I think factually) are listening to something very much like a 'lost cause' narrative only on a winning cause which says, 'Paganism was dying, Christianity was superior under all circumstances and would naturally win under all circumstances.
This is the equivalent of all Southerners were smarter, chivalrous, and manly, and the unpleasantness certainly wasn't over slavery, which wasn't that bad anyway.
And I don't think they bring it in bad faith, but it is a bad faith argument.
It allows Christians to ignore/justify that Classical worship continued into the 9th century. It can ignore the attacks on temples, the murders of righteous pagans like Hypatia. It can excuse and whitewash later events like the Massacre of Verdun. Sure they can point to 'Peaceful conversions', but other than Ireland, there was a sword ready if you didn't peacefully convert.
The idea that Christianity was just better and once people understood it they sensibly converted is just like the Lost Cause argument that allowed Ex Confederates and their descendants to ignore the rights of black people and that the way things are are just swell.
It doesn't matter that it's being given in good faith by people who believe it.