A lot of the complaints about tanks in the alpha arent about damage.
Its about how they're so poor at the tanking part of their job that they come off as redundant in many cases. Outside of their long CD abilities they're just crappy DPS.
That and their rotations for most tanks are boring as hell. Paladin is especially bad in this case. DH too. The rage gen on warrior is god awful too making it boring and the actual tanking part of tanking difficult to impossible during the times when its most needed.
tl;dr: tanks are complaining that they cant tank