I think tanks are fine in SS, the problem I see is that everyone else in the lobbies have no idea how to play with or against them. I often see them running non PVP gear (or not stacking verse) so they are often a really good kill target.
I don’t play prot warrior much but when I do I tend to struggle using my arms gear, if I play a burst dps spec I don’t quiet have enough damage to finish a kill off and if I play a support spec the games go on for too long as I protect the others in the match. Once they open up the conquest cap I do want to play around some more and stack something other than verse.
I did see a blood DK go 6-0 when I was on my healer last week but the guy just played really well and probably deserved it as the climbed the ranks. Everyone else just let him run around doing what he wanted and hard focused on the other DPS.
I think it all comes back to the solo modes blizzard are promoting at the moment, queue up solo with random people, have no voice communication then get a crappy mixed game with no coordination. Make solo queues for casuals just that, non rated play and it would go a long way to fixing PvP. Solo modes are the nail in the coffin for PVP.