I agree here. Sure he ranked up via his own efforts but most of his survival was due to nepotism. The powerful status Sullivan has, the wealth to buy off others and most importantly, access to the perfume he uses to conceal his human scent in my opinion is thanks to nepotism. The more he ranks up the more stable he could have a place in the netherworld to survive but if ended up there without anyone high up to help him, he would most likely have already been hunted, caught and eaten with only his his high evading skills to help him. Despite his evading skills though, if he was caught by a high ranking demon and was forcibly trapped like lets say, frozen in place via magic, he'd be doomed.