That does make me think that he has power equivalent of a lesser god without actually being one. It didn't occur to me to read the MM for more information on him.
I had previously been going off the 5e FR lore where he is still listed as a god. I got even more confused upon reading MtoF where he grants powers to cultists. It might be the whole thing where in the FR he is a god, in Greyhawk, etc, he is still "just" the pre-eminent archdevil.
They already retconned that when they put Tiamat in hell.