Most of the oldest religions of cultures that left records are dead. Religious fervor so great that some were driven, an often succeeded, in driving eachother off the face of the planet… have often been unable to withstand the test of time. There may be a natural turnover rate for religions as old ones die out and new ones form. If there is truly a god, and I think so, I hope he preserves in some form what he feels we need to know through time. I think he will.
If he has, then what may constitute most religons is a fluffy filler that changes with time and angenda, but a core that stays the same