Quote Originally Posted by Balipu View Post
"Ravana also asked for absolute invulnerability from and supremacy over gods, heavenly spirits, other rakshas, serpents, and wild beasts. Contemptuous of mortal men, he did not ask for protection from these. Brahma granted him these boons in addition to his 10 severed heads and great strength by way of knowledge of divine weapons and magic."

In game this was handwaved with Shiva not having enough aether when fighitng Ravana, plus his inexperience with fighitng other primals, but there was no way anyone but a mortal could have defeated Ravana.
That's assuming the devs even take that into consideration. Final Fantasy, as a series, has a tendency to simply use names and likenesses of mythological gods and beasts, but they form their own lore related to them. I don't think Shiva's failure has anything to do with Ravana being strong vs gods and weak vs man, it was Ysayle being over-confident and reckless.