outhouse
Atheistically
It really isn't. Having it masquerade as something else like they were watered down Jews is just plain disingenuous. You mean like many other Jews at the time? You'd be hard pressed to distinguish St. Peter as anything but Jewish and is even mentioned in some Jewish writings (non-canonical and medieval).
There is nothing of peter at all that has any historicity to the real Galilean Peter.
It is not masquerading anything at all, within a few decades the whole movement was trashing jews blaiming them for Jesus death.
The movement and mythology grew in Hellenistic Judaism, which was a group that was never fully Jewish. They were Proselytes at best.
It was a group that wanted nothing to do with traditional Judaism, but wanted the one god.