Personally, I'd say Divine Rank 0 would be a Demi-God. More than mortal, but not actually a proper God. No portfolio, no divine mandates, no ability to give paradox the finger and say "I'm a diety, I don't have to deal with you", nothing like that.
Likewise, I'd say that DivRank 0 is the glass ceiling for ascended heroes, children of gods, upraised divine servants, etc. You either are a God or you arn't, and if you arn't, you can't become one just by putting in extra hours at the office and gunning for a promotion. Mortals and their ilk can Become, but actual Gods just Are.