Belhi's right... Of course Rhalgr is worshiped by many people, but do you really believe that everyone everywhere has the exact same idea od Rhalgr ? The conceptual idea of a god is just too complex, given how many people describe it with different, to concretely exist. Titan is never exactly the same when he's summoned : Sometimes he wants to protect the kobolds, sometimes he's grieving for his parents, and sometimes, he wants to destroy everything. Bestial primals are extremely simple because at each summoning, they only exist for one purpose.

It will be the same for Rhalgr. This primal won't be Rhalgr, it will be the idea of Rhalgr Ilberd has.