[Kameron8]

Life Drain might look great on paper, but it forces the user into a risky attrition game. Believe it or not, this skill is actually suicide against glass cannon archetypes, due to their typically low HP; it will only work well against tanky builds. (It may also work as a finisher skill, provided that going into melee range is a plausible tactic)

It's also a vital piece to keep a cornered Lich alive, given their crippled HP and all.

That all being said, in the absence of detailed examples, I'd say to just leave Life Drain as it is.

It's terrible against glass cannons, but it all but gives you free wins against tanks. Liches will never run out of FP, so this will generally not bother them in the least. There's no reason vampires should be allowed to gain 100 health, and deal 100 damage for free with no penalty against any class, no matter what. A FP cost hit is marginal in the scheme of things.