Not sure if you tested the raids with all the classes but to me it seems impossible to kill Kel'Thuzad on cleric with legendary equip+potion+lvl 10 allies, gonna try some more with rogue now, though he was doing worse than cleric for the lower raid bosses :(
I think there is a bug with rogue skill adrenaline rush.
It only lasts for 5secs and gives 100% atkspeed increase starting from lvl 1...and no further increases with more points added
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I cleared the raid with all classes, some did need higher level allies than other though.