Hey all, Cursed Mistweaver here, so yes I'm gunna be a bit salty. Let's say we're in the 1400-1700 range of RBGs and Arena as of December. Before the difference became insurmountable. Let's presume a base 34k HP around 210 ilvl. A Mistweaver, Disc Priest and Resto Druid walk into a bar. 3 non-descript melee each turn to engages them before applying a 3s burst window.
The Mistweaver pops Fortifying Brew and Life Cocoon. They gains 5.1k max and current HP and a 29k absorb. In this moment they soar to 80k EHP, which falls to 46k EHP once Cocoon is popped, which obviously happens in a single GCD. This particular Monk runs with Diffuse Magic because they saw a nearby Fire Mage and had aspirations of surviving long enough for that to matter, plus I didn't want to do the calculus to simulate the variable limits on Dampen Harm since it doesn't matter to the final argument. Arguably, this Monk could run Healing Elixir and add 6/12k to that burst recovery, but that would be pointless and incorrect since it can't be used under subsequent CC and it doesn't auto-trigger now.
The Resto Druid is in Guardian Affinity, taking 6% less damage baseline. They trinket and then transform into Bear Form and hit Barkskin, Ironbark and Renewal. In this moment they jump to a similar HP but also get the additional armour and and end up at around 70k EHP but with a % based ~10k instant recovery. However, unlike Life Cocoon's benefit to EHP, the total of ~40% damage reductions remain in place and so they enjoy the benefit of 78k EHP for 5-6 more GCDs.
Then the Disc Priest laughs. They have Fortitude buff and so already sit at around 37k max HP. They cast a single PW:S on themselves for a meagre 3.5k, but granting them atonement. Let's take Lenience for that 3% damage reduction because we're presuming nobody will be able to hard-cast for 3s, so Spirit Shell is mooted. Throw in 15% physical damage reduction from Strength of Soul. Focused Will kicks in and adds another 15% physical damage reduction from the same hit. For shits and giggles they also throw down PW: Barrier for 50% damage reduction and and pop Pain Suppression on themselves for another 40%. Desperate Prayer brings them to around 43k HP. Percentages multiply, not add, so they're sitting at around 79% damage reduction. Desperate Prayer brings them to around 43k max and current HP. The Disc Priest now has 222k EHP. A second melee attack pops through that bubble, but grants a second stack of Focused Will so they've broken even against the melee. The Disc Priest still has 208k EHP.
15k DPS is required to kill the Mistweaver within 3 seconds once Cocoon is popped...
...Pretending they don't have Expel Harm or Renewing Mist available.
26k DPS is required to kill the Resto Druid within 3 seconds...
...Pretending they don't have *deep breath* Cenarion Ward, Swiftmend, Overgrowth or NS available.
69k DPS is required to kill the Disc Priest within 3 seconds once PW:S is popped...
...Pretending they don't have Rapture and Ultimate Radiance or Purified Resolve.
69 (nice) is a number 4.6x higher than 15. Blizzard see this and decide that Roll is worth 80% less EHP because, as a dragon once pointed said, 1.5s of being out of range is 100% damage reduction, never minding that Roll (presuming Tiger's Lust is the talent of choice) does not escape the problematic melee abilities providing the 75k globals. They decide the real problem is that Life Cocoon needs a 15s cooldown reduction and that will fix the obvious problem here.
In the corner, a resto shaman teases me for not being able to do the calculus required to estimate the EHP of a class under Spirit Link Totem, but it's presumed they're still in a much better situation that MW because their Healing Elixir still automatically pops at 35% HP and when under CC. And Astral Shift provides an immense 40% damage reduction and Ancestral Vigor grants only 5% slightly less max HP than Fortifying Brew, but with 100% up-time and party wide.
I'm sorry, I know this is just more burst meta QQ, and that this particular problem is only further amplified by many other design imbalances on the cards. And I didn't factor in the effect of Conduits and Legendary options. Honestly, those are smaller contributions than the core kit problems, and they can more easily be changed within the space of a balance patch. And I know I'm far from the only MW who has pointed out the problem. And I know people almost universally agree with the problem so adding more detail to it doesn't really contribute to anything.
But I wanted to point out just the sheer discrepancy in EHP and actually quantify the main problem here. Blizzard could double Life Cocoon's absorb AND the HP and Reduction of Fortifying Brew. They could do this and we'd still only come in equal to a Resto Druid's EHP in Bear Form once Cocoon is popped. Never mind that their instant and passive healing far exceeds ours. Never mind that large parts of MW's design requires us to be sustaining in melee for Chi-Ji and the Ancient Teachings Legendary; meaning we need to have a much higher base EHP by design. Disc operates on a similar design intent as MW but can operate from range; fair play, they don't have the mobility of the other healers, it doesn't really matter when they have that many survival CDs to compensate. Especially in the burst meta where anything under 2200 rating is only about surviving those opener windows.
Don't tell me to play better. Don't tell me to use my cooldowns differently. I have. I know what I'm doing. I've tried. It was manageable until non-scalar damage reductions and heals (% based) totally eclipsed things like Life Cocoon that do SP-based healings/absorbs. But that's the entire meta now: You either have the most % based scaling or you don't.
Edit: I forgot to multiply the Resto Damage Reductions so the image should state 40% damage reduction rather than 46%, for a total of 70k EHP instead of 78k (for all the difference it makes) but I've updated the body text to reflect this.