I don't see the longevity of a belief system as necessarily deriving from its correctness or being based on something real. I can offer examples suggesting that this is true for belief systems lasting a few hundred years. I see nothing wrong with extrapolating this to belief systems that are a few thousand years old.
This puts me in disagreement with people who seem to believe that all belief systems that are old enough had to have a basis in fact or they wouldn't have lasted.
Cheers,
Ben