I see lots of people complaining about the transformation part of this ultimate.
What if the character model still changed to the blood scion one, but your character retained their proportions and size?
This way there would still be a definite physical change to represent the temporary ascension and power surge, but your character would keep some of their individuality. If your character is a giant hulking beast, your vampire form will represent that. Same for if your character is more lithe and dexterous looking.