As we say in Russia, its better to have a pigeon in your hands than an eagle in the skies =), so until Legion goes live and Blizzard won't fuk or nerf Ret, I won't believe that Ret will be one of the Best end game scaling Specs, hence until then the eagle will remain in the skies
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The reason so many Wars use BS and also the reason it is superior to ashes (from PvP pov) because you can use it as a "oh shit" button, you become immune to cc,snare so if u know a inc DF or KS + burst inc from RMD, u can pop the BS and get the hell away behind pillar, same thing if enemy healer is low on HP and u want to score a kill, pop BS and no1 can peel or cc you, that is why it is so popular and usable in PvP. Ret on other hand =) one of the easiest dps classes to peel and cc, hence even though ashes does similar dmg to BS, but it is vastly inferior to it in PvP.
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As i posted a while while back, i believe Retribution should have a passive ability (as our lvl 100 talent instead of Holy Wrath) that the more HP we are missing, we gain higher dmg % + haste. So lets say if we are missing 45% hp, our dmg increased by 15% and Haste increased by 15%. if we are missing 90% hp our dmg increased by 30% and haste by 30%. Of course numbers need to be adjusted but something like that. since THIS will be a true Retribution: If you choose to tunnel Ret, then fine we will punish you with every extra % of our hp is missing ';..;' mwuahaha let the blood flow free!