Monster Mythology disagreeing with you there...
Doresain was a boss in the "Kingdom of the Ghouls" adventure (Dungeon #70)
It's the ultimate proof he wasn't a deity back then: in the 2E, even the weakest deity in the game could wipe the floor with a party of arbitrary high level and numbers
As you mentioned below, "doesn't ≠ couldn't"
But let me point also: people who worship Lady on the Planes getting their spells just fine...
Just because we unaware of her portfolio, it doesn't mean she don't have one
This part always was inconsistent:
Who the heck worships Elemental deities? Yet they're not just don't starving, but, actually, among the strongest...
Deities such as Gorellik and Ramenos are practically not worshiped at all. While neither of them are "fine", they're still not "starved to death" yet...
Orcus managed to be a deity with just one worshiper (Quah-Nomag)!
Also, if lack of worshipers makes deities weaker, then why Tharizdun is still the strongest god ever? And why Doresain isn't Overgod yet - with his untold billions of worshipers?
Let alone the Mythos deities...