Aside from Bahamut, Enkidu, Thordan, and the Bozjan queen whose name escapes me just now, we have no irrefutable evidence that any of the primals ever actually existed beyond folklore before being summoned.

Good King Moogle Mogg is a strong maybe, since he's just a bigger moogle; Ravana's physical form seems to be based on an Allagan construct (seen in the Fractal Continuum as a boss), but it's never really addressed; and Susano may or may not count as a primal at all, if there's any real difference between a primal and a kami.

And Alexander is a weird case, because the primal is based on the folklore based on the primal because time loop shenanigans, I don't want to think about it too hard.