Key-word, "were". You have this laundry list of "conditions" that apparently a vampire HAS to uphold to be a vampire, but you base it only on a consensus of ancient myths and folklore. There's been many interpretation since then that does not meet all your requirements. Myths change with time. As with many other definitions, the main definition of vampire is something that "feels" like a vampire. It's an intangible feeling of association that people have. People simply have some implied notion of what is a vampire, and the only shared trait here seems to be that they leech life-force (you are right that it doesn't have to be blood).Dr. Paine said:those were the key three traits to actual vampires.
So let's bring some hypothetical examples:
Is someone that has to suck human blood, and is hurt by the sunlight, but is no stronger or longer lived than a human a vampire?
Is someone that sucks blood, is nocturnal but only mildly bothered by sunlight, and has no real weaknesses, except perhaps a stake in the heart (which isn't really that much of a weakness since people die from that too) a vampire?
Is anyone that meets the other criteria, but is "near-invincible" rather than just "immortal, but with weaknesses" not a vampire?
The main character in Hellsing anime, for instance, lives of donor-blood, though he goes without for 30 years without consequence, sunlight just bothers him, and he can only die by getting killed one time for each person he's sucked from (some million) or a stake through the heart. He also happens to have several odd powers and strength several times above your average vampire. I haven't heard anyone complain about his status as a vampire, and even if there has, it hasn't been the massive outcry that Twillight has gotten, since it's just people hating the books/movies because they're badly written, and then people trying to find all sorts of other, auxiliary arguments for why they're so bad.