Dark Kight again, i know there are other post but lets push it

[Tunda]

You absolutely can design a tank around HP spending. Getting really tired of this myth because it really shows how shallow some here are with design knowledge.

Fundamentally, just like PvP DRK, a tank with HP spending as a mechanic needs proportional amounts of sustain, either through healing potency or lifesteal. To make HP spending not go completely out of hand, you need to cap it in some way other than just HP (other resources, CD, procs) so you can't just tell your healer to dump everything on you to max your damage, the design goal is self-sufficient HP spending. Here some ideas for sustain:

• Lifesteal buff that on average will give you about 1.3x - 1.5x the HP needed for a spender + some leeway for defensive purposes (short CD, short duration)
• Dreadspikes effect where you gain 1.5x - 2.0x the HP you just took as damage (single hit timed). You gotta mitigate less but get more sustain out of it.
• Stable heal effects, either through resource actions (Blood skills having Cure potency) or timed HP recovery (Sole Survivor) for a burst of HP
• And ofc we can't forget what our dear Living Dead does.

What is important is that the sustain skills do not "just" fuel HP spending, but come with additional sustain for defensive benefit. Now here are some things you could make for HP spending:

• Think TBN, but: drains 20% of max HP, gives you 40% of max HP as shield. Moderate cooldown, only for self (lifesteal synergy)
• Dark Arts, drains 25%, enhances or morphs the next weaponskill/ability to a stronger or different version (maybe multiple stacks? Short CD gate like 15-40s)
• "Dilution", drains 10-15%, expands certain abilities to AOE that could not AOE before at lesser power (defensives too)

Of course, you could explore the avenue of MP and HP having interplay too, namely MP being usable for frequent access to lifesteal (like the short CD I mentioned) and certain HP actions granting MP for example. So you could create three systems:

HP <--> MP
HP <--> Blood
MP <--> Blood

This is just a napkin math and design concept I pulled out of the hat with minimal time investment, but I want to drive home the point that you can absolutely make HP spending a mechanic for tanks WITHOUT making the tank be a liability for having or using them.

I agree with you,

I have been playing RPG CO-OP games and I understand this can be exist but..

developers can't balance such a system without blowing the game

developers play the safe side so they don't want to anger small portion of players