I think you might be onto something here. I've had the pleasure of playing DPS, tank and healer in the PvP endgame and I can safely conclude that healers really do have a remarkably easier time in PvP matches, and can last quite well on their own. In fact, my scoundrel has been able to last quite a lot longer when being ganked than my shadow -- and this is even when my shadow supposedly had on better gear (supposedly). I should also note that I have been playing my tank-build shadow much longer in PvP than the scoundrel. At the moment, I'm finding less and less incentive to play the tank in PvP.
Now, let's just look at the endgame stats. In terms of medals earned and points achieved by doing protection, there is not much incentive to do these normal tank related duties. A good tank, as they get up to speed in the game and acquire equipment, would normally have to sacrifice doing damage for the sake of shoring up other stats -- particularly endurance and defense so that they can do their protective jobs properly. Given that the game has evolved more towards rewarding damage (i,e, DPS), why would any player in their right mind consider anything other than a healer or a DPS for PvP?
Lastly, let's consider one of the major roles usually given to tanks -- guarding the team's nodes / flag while offense tries to take the other nodes / flag. The rewards for any player choosing to do this is poor -- regardless of whether they are a tank or not. And, I am starting to see this reflected in PvP where players are choosing not to guard the easy flag / node usually granted the team for the sake of gaining more medals, valour, credits and experience by beating up other players. What kind of incentive is there to be the lone guardian of a node, when you can further your toon's "gaming career" by not playing as a team member? (Granted, it's often different in ranked gameplay because the team's stake as a whole is clearer - but the fact that it is slow to trickle into the regular PvP, hints that the system is not quite balanced.)
Grue
P.S. Could someone please compare the War-Hero with the Elite War-Hero gear on Sage/Shadow side? It may be just me but I keep getting the impression that some gear doesn't really do much to improve your stats when you upgrade (e.g., implants).