Your a and b are by no means certain. It is uncertain whether or not Moses existed. We really do not know who started Judaism. And as your pair of options indicate, we do not know who started Christianity either. So we cannot be certain that they were started by an individual or not.
Additionally, with the others, like Mormonism, although we know that Joseph Smith started it officially, that does not mean that there were not confederates in on the scam. Indeed, it seems likely that some of them were, since, supposedly, there were three witnesses who claimed an angel showed them the tablets in a vision:
https://en.wikipedia.org/wiki/Three_Witnesses
And there were supposedly eight more who said that they saw the golden plates:
https://en.wikipedia.org/wiki/Eight_Witnesses
See also:
https://en.wikipedia.org/wiki/Book_of_Mormon_witnesses
Of course, we can speculate about how many of them were in on the scam, and how many of them were duped, but it is difficult to know precisely what the status of everyone was. In short, we do not know if Mormonism was started by a group or committee, or if the scheme was purely dreamed up by Joseph Smith, who later added confederates who were in on the scheme, though it seems likely that some of the early converts were simply stupid fools who were easily suckered into believing Smith's nonsense. But it isn't as if the machinations of Smith were open to public scrutiny, so we are left without knowing exactly who dreamed up which bits of Mormonism.
Additionally, with the others, like Mormonism, although we know that Joseph Smith started it officially, that does not mean that there were not confederates in on the scam. Indeed, it seems likely that some of them were, since, supposedly, there were three witnesses who claimed an angel showed them the tablets in a vision:
https://en.wikipedia.org/wiki/Three_Witnesses
And there were supposedly eight more who said that they saw the golden plates:
https://en.wikipedia.org/wiki/Eight_Witnesses
See also:
https://en.wikipedia.org/wiki/Book_of_Mormon_witnesses
Of course, we can speculate about how many of them were in on the scam, and how many of them were duped, but it is difficult to know precisely what the status of everyone was. In short, we do not know if Mormonism was started by a group or committee, or if the scheme was purely dreamed up by Joseph Smith, who later added confederates who were in on the scheme, though it seems likely that some of the early converts were simply stupid fools who were easily suckered into believing Smith's nonsense. But it isn't as if the machinations of Smith were open to public scrutiny, so we are left without knowing exactly who dreamed up which bits of Mormonism.
"A wise man ... proportions his belief to the evidence."
— David Hume, An Enquiry Concerning Human Understanding, Section X, Part I.
