personally i firmly stand in the camp that the increased regular ability cost and the complete loss of health regen needs to be removed and changed with personally here a basic concept for something i feel would suit the vampire race better and make vampire something people would ACTUALLY wanna play. firstly, i would fully change the stages passive to completely new pros and cons with firstly, the ability cost increase for regular abilites would be removed with the decrease in cost from vampire abilites would be kept. secondly, i would say that the fire weakness should be removed and instead changed to elongate the effects of dmg over time effects OR increase the effect (this is to partially offset the strength i would give vamps making them need to either play necro builds to reduce the dot dmg or to be warry of any dot dmg they come across.) of all dot dmg to reflect the notion that against a creature who regenerates, using attacks that leave a lingering damage over time to constatly eat away at their healed health is a standard to defeat them. third, the health regen nerf is going to be removed all together and replaced with a ramping flat weapon and spell dmg nerf to all non vampire abilites with lastly, i would also add a ramping boost to health regen which will make sense with the one ability i would desperately want changed.
now as for the changes to the primary ability i think should become a vamp mainstay but also another quasi nerf if they dont play smart with it being that the frenzy skill would become the first skill you earn as a vampire and would be changed from a ramping health cost in exchange for a flat weapon and spell dmg boost to granting a flat percentage dmg buff of perhaps something like 10% AND boosting the duration of all buffs and debuffs applied by specifically your abilites (regular and vampire) by 5 seconds with the cost would be that all abilites would now have a health cost as well equal to perhaps something from 25% to maybe even 75% of the abilites total cost on top of its normal cost which of course means you can lower this negative by lowering the abilties cost which with all normal abilites no longer having their cost inflated and in fact, the vampire abilites including this new frenzy rework all getting a decrease the higher you vampire stage means that you would be learning to channel your blood magic better to also increase the strength and longevity of your magics by enhancing it with the power of your own blood getting around a vampire normally being weak actually in normal magic (kinda spinning something similar to vampire the masquerades tremere but with normal magic still being a thing you can use by saying that vampires loose their connection the magicka of the world around them but gain the ability to more readily draw on the power within their own blood and take advantage of their bodies increased regenerative ability to ignore the cost of using their own lifeforce so recklessly)
all in all, this would push people to perhaps decide playing on the riskier side and having a health cost on all abilites or perhaps even maybe changing it so it makes ALL abilties costs require health AND perhaps to coutner balance this, while frenzy is active, all your weapon and spell damage scales with your hp at a perhaps 10% weaker rate than with magicka and stamina so its not a flat increase but also lets you max out your health and truly give into the blood mage theme and add some even better fun to the concept of playing such a risk reward way with perhaps one last effect of frenzy would be to grant all sources of lifesteal a 25% boost to help ensure you can still actually regain more health than you spend to cast abilites like repeating strikes or hungry scythe for example.