Reev what you're doing doesn't make complete sense to me, its more valuable to compare the effect of x amount of ratings have assuming a certain base of stats, since you always will have a certain amount of stats anyway. I agree with you that the value of block doesn't look great specially if they would implement DR on it.
The value of avoidance and block is the amount of damage they reduce multiplied by the percentages of attacks they effect.
For avoidance this would be 100%*percentage of attacks effected
For block this would be 30%(or more)*percentage block*(100%-avoidance)
Depending on the average blockvalue block already reduces 3,3 times less damage and depending on avoidance it will effect 1,4 (1/0,7) times less attacks.
It's also slightly more complicated since an avoided attack can replace a block instead of a normal hit in the 2 roll system.
edit: avoidance would be (100%-(blockvalue*blockchance))*percentage of attacks effected
With my current gear I have like ~38% avoidance and ~64% block even disregarding potential DRs on block and having 100% uptime on SB the boss will still be hitting me in the face ~11% of the time. Hope shield tanks get an armour/HP buff to bring them level of DKs and Druids
The only way to buff shield tanks for their gimpy Mastery is either flat damage reduction (which would then also work on magic damage, making them better dragon breath tanks) or ... shield armor (all plate tanking stuff can be used by DKs). So you'ld be a shitty tank until that tanking shield of that tier drops (because let's face it, we'll only ever see a single shield per tier)
Time to hit the math and see how mastery competes against avoidance this weekend :)
What really, really bothers me about the new block system is SHoR and Shield Slam only block the "next" attack. This means that if you're tanking one mob, Mastery is the worst stat, (because it can't apply to your guaranteed block) but if you're tanking more than one mob, Mastery is the best stat. Are you going to have two sets of gear that you have to switch between for one mob/multiple mob fights? Are you going to go reforge everything between bosses? It's ridiculous. Paladins are already going to have to respec their 45 and 90 talents from boss to boss for max effectiveness, now they're adding this?
When you're tanking one mob only, this makes mastery really really bad, as you get a free block every 6 seconds so your mastery doesn't have any effect at all except for when the mob bypasses your avoidance twice in six seconds. However when you're tanking more than one mob mastery suddenly becomes the best stat since you're taking more attacks and the SS/SHoR effect still only blocks one hit every 6 sec.
AFAIK That functionality was changed. Six seconds of +25% block chance is what you get now. I still don't get the whole i take more hits so block more hits. but statistically you're still going to be blocking the same proportion of hits, it's just the amount of incoming attacks that changes.
Warriors: (100 - 20) / 1.5 - 8 = 45.33~
Paladins: (100 - 5) / 2.25 - 8 = 34.22~
That's a lot of mastery, gentlemen.
Using the level 85 values, we are talking about 8100 mastery rating for a warrior, and 6100 rating for a paladin. And that is ignoring any DR.
The problem is that mastery gets much much better in terms of overall damage reduction the more of it you have. So for the same reason they put DR on armor and avoidance I'm sure they will likely go through with this change.
On the other hand this new system they are proposing, mastery gets much much worse the more avoidance you have, so if they DO put in DR then all mastery will do is get worse with gear.
Shieldblock from warriors is 25% blockchance, I've not kept up with the pally changes but what you quoted seems overpowered compared to shieldblock, would be more logical if it was just 25% increased blockvalue but who knows what blizzard is doing.
Perhaps the changes can be seen in the light of striving towards the "active mitigation"-model that was spoken about as compensation for threat made obsolete?
Blizzard doesn't want any capping by gearing. But gearing along with skillfully deflecting damange thru a rotation could give a simila result as just gearcapping nowadays? To me that sounds like a fun way to really be a good tank.
What makes me think that this might not work out is that bad tanks gets punished a lot. Either content must be easy or being a good enough tank must be easy.
However, if it is really just needed for heroic raids and challenge modes. Well it could be win win for everyone type of player!