There is no incentive to feed as a vampire (still), and the cost increases with level makes it unattractive for any PvEr.
There are so few vampire abilities that are attractive for pve dps that you do not get much out of vampire cost reduction. But making new abilitis is hard making small changes to existing ones is a lot easier.
First, return Supernatural Resource Regeneration. The sharp increase in ability cost seems to suggest that there was once a regen passive available. If continued to be where it was before at level 3 vampire it would encourage active feeding and the cost increases would not disadvantage a vampire dps player quite as much.
Eviscerate, is the only dps ability in a vampires kit but one of the morphs is health-based and the other is a melee Magicka skill. This does not make any sense in the current design of the game. Health dps is not a thing (possibility even dangerous if it were) and magicka dps is (almost) all ranged.
So Blood for Blood should be a stamina ability that deals more damage if you are low on hp, Arterial flow should be a ranged ability.
The strange thing is these changes seem so obvious that it almost feels like these were the original plans that you changed at the last minute is there a reason that this was not implemented?