Given all that, I'm going to highlight some comments I posted elsewhere since it's a question I've seen more than once, most prominently at Blessing of Kings:
However, as I understand it, Resolve means that a tank who is not taking damage is squishier than a tank who is taking damage.It's an interesting question -- but the answer lies in the active mitigation category.
But if the tank is not taking damage, does it really matter that she is squishier?
Or to put it another way, there's an equation that should balance in a successful fight:
Incoming Damage = Healing from Others + Self Healing/Mitigation + Healing/Mitigation from Resolve
Why not just remove the Resolve term? You could directly boost the self healing/mitigation or lower the incoming damage, and the equation would still balance. Removing Resolve would simplify things, and not create weird situations like a successful parry/dodge streak that causes Resolve to drop off.
Balkoth wrote...Rohan then gave a response...
Here's the problem: you're not considering things like Shield Block versus Shield Barrier. Let's say Shield Block reduces damage by 30% for 6 seconds and the boss hits every 2 seconds for 100 damage. Now let's say Shield Barrier absorbs 90 damage.Both of these mitigate the same damage every 6 seconds.
But what if the boss only hits for 50 damage? Now Shield Barrier is twice as strong. Or what if the boss hits for 300 damage? Now Shield Block is three times as strong.
Resolve exists to scale the flat absorbs/heals (like Shield Barrier, Frenzied Regeneration, etc) at the same rate as the percent reductions (like Shield Block, Savage Defense, etc)
Balkoth, if the problem is a mix of percents and flat amounts, wouldn't it better to change abilities to all use percents or all use flat amounts?
To which I responded...
Balkoth wrote...TL;DR version: tanks typically have one active mitigation that reduces damage by a percent and another that heals or absorbs a flat amount of damage and Resolve is needed to keep these at roughly equal power. The heal/absorb still mitigates LESS overall but it's used to mitigate spikes of damage which are dangerous.
Let's say it's all percents and thus Shield Block reduces damage by 30% for 6 seconds and Shield Barrier reduces damage by 90% for 2 seconds (same deal, right?).
But now imagine the boss has an special attack which applies a debuff that makes the next special attack do more (like a breath that deals fire damage and increases fire damage taken by 100%) and this fires every 10 seconds and the debuff lasts 30 seconds.
So you'd swap every 3 stacks, right?
Nope! Because you could use Shield Barrier to reduce that hit which should deal like twice your HP down to 20% of your HP. Even an attack which hit you for eight times your maximum health could be reduced to 80% hit -- which would be a hell of a lot of stacks. In fact, you'd never need to swap. Any hard hit of damage which occurs less often than you can Shield Barrier is irrelevant.
So let's go to the reverse and say we go to flat absorbs. How would that even work for Shield Block?
Absorb a flat amount per second? Then that's less effective against slow attacking bosses which might only hit every 2 seconds and more effective versus fast attacks.
Absorb a flat amount per hit? Then that's less effective against hard hitting bosses and more effective against fast attacks.
Absorb a flat amount? Then that's Shield Barrier.
The best case scenario would be something like using Shield Block builds an absorb shell every second that stacks with itself -- which would mean it becomes TOO powerful if you happen to dodge/parry a few attacks because then it applies that absorption to a single attack.
So then you'd have to do stuff like remove the absorb on a dodge or parry -- except then what if you parry a weak add's attack and then eat a hard boss hit to the face?
Then on top of that you have stuff like Savage Defense which gives a Dodge increase so that's a whole new bag of worms.
...we could just make Shield Barrier absorb more against harder hitting mobs so it stays roughly equal to Shield Block.
The main idea, actually, is that Shield Block is better at mitigating overall damage but Shield Barrier can be used to deal with known spike damage or in case your HP dips low. It's meant to be a tradeoff.