But it takes many decades for someone to rise from parish priest to Pope, and the chances of promotion at each stage is very tiny. I don't think sleeper agents would be practicable in the least.
No - that's talking about a specific person. I'd be fine with putting "WI: Pope Francis converts to Islam" in ASB, but some unnamed Pope is different.
Okay, the very vast majority throughout history, with other groups being accused of not being Christian at all. And the entire Roman Catholic Church - the group in question in this thread here - is in that vast majority.