The premise of this topic is IF a skill line that scales to Max Health and Physical Resistance existed and how it might effect the current meta, future metas, be adjusted and so forth.

This skill line does not exist and is entirely hypothetical. It asks the question of how would it work, not should it be allowed.

The mechanic of Blood Magic is that it is reliant on health sacrifice for cast cost. It's damage type scales on target Physical rists. It is designed in a fashion to have high physical resistance, resistance to disease and poison, and to have little to no defense to magical damage. It is weak to itself and magical builds. It is strong against heavy armor and mid against medium.

The skills I thought of take inspiration from of the Necromancer Class, Night Blade Class, the Vampire skill line and several others
Introduction stage.
Buffs might be in the realm of resource gains but lacks spell and weapon damage increase. Instead we might see physical penetration increase and resistance, Vitality, Life Steal and Toughness being the only two I could think of working for a skill line that targets based on physical resistance of a target.
Debuffs caused would likely be mangle, defile, breach, bleed, weakness, maim and vulnerability

Spammable, Skill 1
Base: Cause x damage base on target's Physical Resistance
cost: x health
cast time: x
range: melee
Melee Morph
Cause x Damage based on target's Physical Resistance, chance to cause bleeding
Cost: x Health
Cast time: x
Range: Melee
Ranged Morph
Cause x Damage based on target's Physical Resistance, Chance to cause Minor Defile
Cost: x health
Cast time: x
Range: 20 meters
CC skill 2
Base: Selected target is slowed by 30% with Minor Maim with x DOT
Cost: X Health
Cast Time: x
Range: 30 meters
Morph 1
Select target is slowed for 60% with Minor Maim, gain Major Expedition with x DOT
Morph 2
Cast an AOE that slows for 40%, enemies are stunned after 3 seconds and take DOT
Heal, Skill 3
Morph 1- self
morph 2- AOE
Ward, Skill 4
Damage shield absorbs physical attacks
Morph 1 Cast on ally
Morph 2 self with extra buffs
Curse Skill 5
Cause life steal and mangle on single target
Morph 1: Major Mangle
Morph 2: Magicka steal.
Ultimate
Create an AOE that does x damage per second that scales with Max Health, Heal for Damage done. After x Time gain Major Toughness for x seconds.
Morph 1- Synergy
Morph 2- CCs enemies.

I am too lazy to think of the passives but I would imagine to make this skill line work they would all be trade offs that give bonuses for how many skills are on a bar, but also make cause vulnerability to magical damage. So this might cause a rather sizable health pool and health regen making a player rely less on magicka and stamina abilities except on a back bar.

I would classify this skill line as one geared towards a tanky DPS that really benefits from a healer. Thank you all for your time.

Edit: To be clear, I would love to hear any and all feed back. Even from those who think it is a terrible idea or not.