In spites of knowing its true weakness, which was destroying the wooden casket that turned it into an immortal, killing the nosferatu turned out to be way more challenging than Uriel anticipated. While it was true that his rank wasn't on par with the nosferatu's horror level, Uriel had faced so many stronger enemies before he simply assumed he would be able to overpower it somehow. But the difference in power between a monster level and an entity level cryptid was nothing compared to the difference between an entity and a horror level cryptid.
Luckily for Uriel, the nosferatu wasn't that combat oriented and its strength came from its ability to turn others into vampires or control them with its eyes, something that, safe for when he was taken by surprise, didn't affect him since he knew how to counter that thanks to his sparing matches with Medusa.