I'm not saying this theory is wrong for all Vampires crimsonmelody, I can't speak for all Vampires because I don't know them, but I don't mind explaining what I mean for me.

I know that I am an energy deficient being because my essence requires the kind of energy that my human body just can't provide, but unfortunately I am one of those hideous creatures who believes that the human part of me is only an outer shell. An overcoat I wear in order to make me acceptable to society. I live in it, I care for it, feed it and get it medical help if it needs it, and I accept it's limitations (though I'm not always happy about them. lol), but that is as much of a connection to it as I have. Therefore I cannot be a human with an anything.
Vampire is what humans call beings like me, it's the word they use to describe me, and since I have no problem with labels that are used to help understand and not ridicule or belittle, I go with the easily understood word Vampire, but there are many energy deficient beings on this forum, and not all of them would identify themselves as a Vampire. They reside in human bodies like me, and take in extra Psi energy to maintain their essence just like me. But they are not creatures like me.
That is why I believe that to classify all Vampires in this way is wrong, because although it does describe many of the Vampires you will meet in forums on the internet, it doesn't describe them all, and the description does not just apply to Vampires, so it is not only an inaccurate description it is also incomplete.
The whole energy deficiency and feeding issue is complicated and I find the way people have of describing Vampires as 'energy deficient humans' dismissive and a bit rude.
Maybe most Vampires don't mind, or maybe most of them agree with this description, I don't know. I only know that it doesn't fit me, and there are quite a few other people I know that it doesn't fit either, so at least I'm in good company.
I believe in the vibrational theory. Science has proven that everything that exists vibrates on a certain set frequency all it's own. Each one is different and so distinguishable from all the rest. I am an essence being who vibrates at such a fast, high and intense rate that extra energy is necessary for me so that I do not feed on the energy the human body needs in order to sustain itself.
I feed on Psi energy because it is everywhere and easy for me to process. I have blood fed in the past, but not for many years now, and I am a vegetarian too so my body really doesn't have the energy to spare for the essence to feed from.
Like I said this is only me, as I know myself. Others may be the same, and some others could be different. Some could even be energy deficient humans.

The Walk-in part of me is even more complicated than this, so I'll leave that for another time.