I dont think you need avoidance working on all magic. I'd prefer there being some situations where stamina is just better (although it happens too much atm and theres not enough the other way).
Really we just need more options with gearing and more varity in damage mechanics than there is in ICC.
In sunwell I was juggling threat / avoidance / eh because you could make meaningful choices with gear and because the different fights challenged tanks and tank survival in different ways.
In ICC with threat and avoidance marginalised, you pick between stamina and armor. Except theres no armor gems, you dont get bonus stamina items like you do with armor and the only enchant choice between the 2 is gloves afaik so the majority of gearing ends up swapping around trinkets. Its just alot less interesting than it used to be imo.
But it already seems like they are trying to make avoidance more desirable in cata. And also make the different stats more distinct (rather than parry being dodge but worse). I just hope they dont make it too bland for the sake of class balance (ie we cant have a fight where say dodge is better because druids would be op).
We all have preferences - and I can understand a desire for a more fluid player response model - but as someone once said in a thread here - WoW is a game of inches - each point individually doesn't amount to much, but multiple a few points across 17 slots, 20 gems, 13 or so enchants, and 5/10/25 party members and you have the difference between beating the enrage timer and not at the leading edge of progression. No matter what the model is, there will be a single perfect possible future (to quote Trance Gemini) that will make those who want more flexibility cringe as they feel forced toward it to maximize player output.
The avoidance / EHP discussion is not a discussion of which should be be done, but of a rebellion to conformity. The answer is put your mouse down and pick up a pencil and paper RPG where you and your friends can create that dynamic world. WoW is a game of numbers. It has predictible outcomes (though RNG doesn't make these set in stone). It will always, no matter what the model is, require an adherence to a precise player model in order to maximize output, and while it may not be much individually, it will be important across 5/10/25 players.
Actually, I think Parry has been nerfed, don't you?
On Parry Success I do have a question, is block also given a chance? So you can parry a swing and then block for additional damage avoidance or will it be like current, where there are basically 5 states - Miss, Dodge, Parry, Block, Full Hit?
If that design stays, where an attack can only be modified by one of Dodge/Parry/Block then I see the following scenarios where Parry is less effective in Cata than in WotLK
Scenario A) Parry - Dodge. Parry first wing, RNG dodge second swing. Total damage avoided 75% in Cata Versus 100% in WotLK (.5 first attack + 1.0 in second for 1.5 out of 2.0)
Scenario B) Parry - Parry. Total damage avoided = 50% in Cata versus 100% in WotLK (.5 first attack + .5 second attack - for 1.0 out of 2.0).
In both of these scenarios you're going to see a reduction in damage take on Parry RNG success.
Maybe I'm wrong (I hope I am) but I see Parry as being nerfed in Cata - though maybe the increase to Block mitigates that to some extent (poor DKs and Bears though).
It does seem though that the change to Parry and Block are keeping in line with the Chill of the Throne Debuff and trying to make damage more even with the difficulty being in responding to spiky damage (Fester 3rd inhale, bonespikes, etc).
Thinking about this subject is reasonably difficult because of the nature of the game:
Avoidance = Over time benefit
Resistance = Over time benefit
Mitigation (RNG) = Over time benefit
Mitigation (Per hit) = Instant benefit
Health = Instant benefit
Our system for hurting and killing tanks relies on a short term basis, a tank will either take more damage than their health + incoming healing will allow for, or they won't. The over time effects may play into this however it is likely that we will encounter a period of damage with insufficient avoidance and pop. Avoidance and other over time effects thus become irrelevant even in a mana limited world (Cataclysm) simply because we need the healing + survival on the short term.
What we instead need to consider is different methods of hurting the tank / raid. The first obvious one is something akin to a danger zone / shield effect like Halo. You take a whole bunch of hits and its fine until you hit the end of your resource pool (shield goes to 0, healing hits a cap or similar) and enter into a danger zone where by hits become more deadly, but we become harder to kill / more cautious. In this kind of system we could threaten tanks on a short term basis and have them blow cooldowns, avoidance trinkets etc in a short period of time to survive. Tanks might gain a set of abilities like:
Offensive: Your avoidance is reduced by 30/40/50% while in this stance, your damage done is increased by 33/66/100%.
Defensive: Your damage done is reduced by 30/40/50%, your avoidance is increased by 33/66/100%
Mixed: You gain no additional benefits
A tank in pure defence cannot hold aggro, a tank in offensive builds aggro well but takes increased damage. When they hit the danger zone type effect a tank drops into defensive only and blows trinkets (allowing us to make ourselves effectively invincible for short periods) making us harder to hurt and less likely to die. You of course need to balance these correctly with periods of spike damage that can still kill a tank if they are silly.
The second way is to make over time effects important. Imagine if all raid members had a third bar (health, Resource, Capacity) representing their capacity to receive magical healing. A regular raid member might sustain 3x their health as capacity, a tank 25x. Each point of healing done reduces your capacity by 1, if your capacity reaches 0 you cannot be healed. At this point over time effects become important as tanks die from hitting that limit. Every hit that doesn't need healed is a point that can be healed later, and the same applies to the raid. Suddenly it becomes important to not stand in fires, and not simply use massed AoE spells for healing except when necessary. The game slows down a lot and people become more focused on saving themselves, defensive abilities in trees become useful again if they can help keep your capacity up.
TLDR: Avoidance and similar are only useful over long periods of time, the damage that kills us is always in short bursts. Until the longer term matters, or we can temporarily up our stats at the cost of others random effects will never be able to realistically overtake fixed survivability ones unless those become stupidly expensive (and what do we do then... no stam no avoidance).