That theory doesn't match with the evidence we have at all. The Pauline letters (the ones considered authentic) show us that there were many early leaders, some of whom clashed with Paul, as well as many different factions of Christian, some of whom Paul disagreed with. 1 Corinthians, for instance, he's talking about different Christians (or rather, proto-Christians) saying they're the followers of different leaders. You also see Paul as a late comer to the movement really try to defend himself as being considered an apostle. And one really has to twist Paul's words to say he's treating Christ as a merely celestial being (Paul even talks about Christ's human brother).

You're also claiming that the proto-Christians weren't working within a messianic Jewish framework (which the academic view of early Christianity fits nicely), but a completely different framework that we neither have evidence of before and that completely disappears afterwards.

Speaking of completely disappearing afterwards - Paul's letters are from ~50 AD, Mark is ~70 AD. So you have still have to posit a massive and seemingly unified (even though the early Christians were hardly unified) agreement to adopt the human narrative, since soon after we get a lot of information about heresies, and lots of criticisms about Christianity, but no one is aware that it (supposedly) was as a completely separate religion within living memory.

It's just a very strange theory, one that posits a completely different religion suddenly appearing and disappearing, and seems to be based solely on ignoring most of the content of the Pauline letters, twist the words of some of the others, and just making up the rest whole clothe. It's about as historical as Dan Brown's version of Christianity, and has as much scholarly support.