Skyrim vampirism is "Vampire lite". They're weaker, and there are almost no penalties for being one. I really dislike it.
But the basic framework of "starve, get stronger, feed, get weaker" makes sense. Blood is life. The more one drinks it the closer they are to mortality.
Exactly this. Human blood brings vampires closer to being human. Thus, fewer vampire powers. They don't need to feed for strength, they are immortal. Vampires spend thousands of years locked up in caves and then come at you, axe swinging, just fine. Food is irrelevant to their strength. Their proximity to mortality is what makes them stronger or weaker.
And that goes against everything that a vampire represents, in my mind. Using a cop out excuse like "hey, anything is possible with magic!" doesn't excuse what is in my mind a poor design choice.
If they decided to make Destruction magic heal people, would you be pleased with the excuse "it's magic!"?
Last time I checked, vampires are fictional. That means there's no reality to emulate, nothing that a vampire actually "represents." Every major story about a vampire is different from all the others in some way or another. Would you like it if vampires in TES could turn into bats, just because some lore out there says they can?
No. That's not how fictional fantasy creatures work. Every major story that uses the theme of "vampire" gets to come up with their own theory of how the mechanics work. That is, in fact, why such things are so endearing over the centuries, each new culture and generation can adjust the lore however they like.
If you think the vampires in TES are sub-par because they aren't like... "normal vampires" or something, I'd challenge you to find consistent evidence that there is such a thing as a "normal vampire" in the first place.