I hear this a lot and have to disagree with one point for sure: The dmg output is nowhere near the same in Tank spec. I do admit I mostly play my juggernaut so I cant say this with certainty for the other classes but at least for the assassin I am pretty sure it is true as well. While you can do a good amount of damage (and dps) in tank specc, you're getting nowhere near of killing anything in a reasonable amount of time and you certainly won't kill anything with the slightest amounts of continous healing. There is a threshhold of dps you have to do to kill someone.
Are skanks useful? Yes indeed I think so. Are they overpowered? Maybe, I haven't played any ranked so far so I won't judge that at all. But to say they do similar dps compared to a dps spec is objectively wrong.
Back to the topic at hand: I really do agree that the selfhealing capabilities of mercs/mandos are way too high at the moment. But in my opinion you can't generalize that for the other classes. While juggs/guardians have a strong healing ability as well, they don't have a simultaneous dmg reduction buff and, now for me that is most important, they are a melee class.
And I feel (note, this is just a subjective observation from my pvp ecperiences, I don't have any numbers to back that claim up) that Juggs/Guardians are way easier to kill (and to control) than a merc/mando.
tl;dr: don't judge all dps classes based on the current op'ness of certain few classes