For a legend like Vanescula healing is extremely easy with all of her health stealing cards. I really don't think it is necessary for her to have a card with this much sustain potential. at 6 attack and 4 health it is quite easy to kill, especially with vanescula being able to stack AP easilly. With a 2 health reward and on top of that you get to heal equal to the attack of your opponenent's next creature x2.Also, even if you can't one hit it if your opponent has a creature with 3 or more attack you still gain value.

I get that it depends on your opponent but many commonly used creatures will give you insane heals, such as tztokjad, Ket-zek, and various others.