Currently at:
Stage 1 - 2 health per second cost - 6 magicka per second
Stage 2 - 3 health per second cost - 10 magicka per second
Stage 3 - 4 health per second cost - 13 magicka per second
Stage 4 - 5 health per second cost - 17 magicka per second
Should be more like this imo
Stage 1 - 5 health per second cost - 6 magicka per second
Stage 2 - 10 health per second cost - 13 magicka per second
Stage 3 - 15 health per second cost - 17 magicka per second
Stage 4 - 20 health per second cost - 23 magicka per second
I know the vampire lord version is pretty powerful when Serana is not your follower but this ability should be tweaked a bit so it is a viable option. I wouldn't even mind if it scaled with your level so it can still be used late game to some degree.
****Note: Vampiric Drain spell does not improve the Destruction skill either.