Quaking, Bursting, Explosive, Grievous, Void Emissaries, etc all do damage based on your maximum HP. The devs probably did this to make tuning easy, but it fundamentally doesn’t make sense to do this in an RPG:
1. It invalidates gear progression
The more gear you get, the more stamina you have, the more damage you take from affixes. You can never outgear it. As a side effect, on weeks with a lot of affix damage, an undergeared healer will have it easier healing a party with ilvl similar to his own than healing a well-geared party.
2. It punishes classes for having more HP
Having a high HP pool is supposed to be a good thing for survival, but when somebody in the party buffs stamina, all affix damage just increased by 10%. On Bursting weeks I usually skip buffing Fortitude.
Similarly, using defensives such as Rallying Cry, Desperate Prayer and Last Stand before a high Bursting stack makes you less likely to survive.
Tanks are supposed to take less damage from hits than the rest of the party, but they take more damage from affixes due to having more HP. Tanks with naturally high health pools take more affix damage than mitigation-focused tanks.
3. Keystone difficulty
A third problem specific to WoW is that these affixes have the same difficulty regardless of keystone level. I remember in a previous season we had the affix combination Quaking+Bursting. During this week, I did a +15 on my main and a +7 on my alt and I did almost the same overall HPS in both runs due to the vast majority of damage coming from those two affixes.
Affixes should have static damage values just like everything else. There are plenty of ways to tune them so that they work for everyone. For example you could make Quaking deal X damage, scaling with keystone level. If the damage gets out of hand in high keys, put a cap on it at +15 or so.
