I won't change my opinion Total. I don't know where you pulled 18 seconds from..are you suggesting that during 15 seconds of EB, you'll only generate 3 stacks if you are going for critt build? And it's not that you are doing tank swaps every 15 seconds so the rest of the stacks would go wasted. But to go from fight to fight just to see how much time you will actually tank a swings. On immerseus, either you'll tank the boss, or tank the adds. During intermission there is none damage you could reduce with mastery. On protectors you are tanking one boss most of the time (exception if you tanking he goes DM phase or rook and vengeful strikes). On norushen you'll tank add inside, then boss, then adds. Sha of Pride is maybe an example where yous witch very often, but again, there isn't any notable damage that fill your stagger fast, let's face it, purifying green or weak yellow stagger would be waste of chi. On galakras you are constantly tanking, either tower or downstairs. Juggernaut is maybe exception where I would put mastery ahead, mostly because of bombs, but I never felt bombs are the issue on Juggernaut, more like falling damage and dot that rapes you. On shamans you are constantly tanking one of the bosses. Nazgrim might be exception, but again you switch evey 30 seconds. Malkorok might favor mastery because of blood rage. On spoils you will constantly tank one side. Thok hurts like hell, I agree mastery could favor it there. On siegecrafter you are switching boss add boss add and all stacks you receive you can precast with guard, zen med, fort brew, diffuse magic, dampen harm. Klaxxi is hard hitting, even though you're tanking one boss constantly, I would switch to mastery build during bleeding edge progression. And on Garrosh, yes, he hits like truck but dot rapes you as fuck, and mastery won't help you with dot.
You're tanking a lot tbh, and it's not that you are 50% of most of the fights inactive on tanking, and special abilities such as execute, Immerseus cone, eletrostatic shock is predictable and easy to deal with without mastery build.
And I don't know why you are pulling level 100 talent and WoD in discussion if poster started thread to ask for stat prio in current build. I agree with some stuff other people said, might be wrong at some points. If everyone was right all the time, discussion wouldn't exist. But your counterarguments such as magic damage, lvl 100 talents doesn't make sense.
If we were talking about WoD, I would agree mastery is better.
You see it here and on every second topic when discussion appears that there is literally 10 different opinions on everything. Think we got far from original topic and just confused original poster with this discussion.