It's not entirely useless. All of the mods/enhancements stack a ton of endurance, so more endurance will keep you alive longer in pvp. Furthermore, if you're fighting a marksmanship sniper/carnage mara/deception sin (mostly), stacking a ton of defense/shield will help you to avoid a lot of the melee/ranged attacks or at least shield/absorb what you don't avoid. So it has some benefit.
Of course, if you're going up against an operative/sorc/etc classes that use exclusively force/tech attacks, the shield/absorb/defense won't do anything, but your armor rating will reduce the amount of damage you take and the extra endurance will keep you alive longer to take more hits.
I have a ton of endurance on my jugg tank, helps me stay alive a lot longer, I do very little damage, but I stay alive longer, so definitely useful in huttball.
I just think it's sad that tanks have to resort to using dps gear now because survival gear doesn't really help against force/tech damage, at least dps gear gives them something to rely on, but like I said in my previous post above it would be great if tanks had an ability to push off force/tech damage or at least have a chance to since it takes so much out of us.