Using those guidelines, I think you could make an argument for Hercules (Marvel's), Captain Britain, Namor, and Orion. Never underestimate a writer's desire to pump up a favorite character. Representing something bigger than yourself is exactly the kind of thing I can see becoming a slippery slope. It doesn't have to become one, but again, writers and their fave characters.
You could use further restrictions to keep the list thinner. Heck, you can put down "must believe in Odin as a god" to keep the list to just Thor. But the slippery slope isn't the main reason I dislike giving a specific definition of worthiness, anyway. My main reason is that keeping it vague gives it a grandiose quality that a list of qualifications doesn't. It's similar to the principle of never showing a horribly scarred character's face. Some things are more powerful when kept to the imagination.