Deception Assassin are the best 1v1 class in the game. And a skilled assassin wins most of them without stealth even. If that is what you are on about, fine, but pvp especially non objective based pvp is not 1v1. Even in objective based pvp regular wzs you hardly get one 1v1s mostly with ninja capping and node guarding. So it is a mini game in the macro game of a wz. In ranked 8v8 you can be sure the off nodes are guarded by a stealther as well, since it would be stupid to do otherwise, so the only really 1v1s in those matches are between stealthers...
but the 1v1 will play even less of a role in arenas, and so does stealth which is a 1v1 boost.
Both Deception and Concealment are single target burst specs designed for 1v1. Concealment is already in such a horrible place that even in normals you end up frustrated very often, because if you dont crit you hit like a nuddle and have about the survivablity of an unbubbled sage, just that you have into melee to do any damage. Nerfing Deception to the ground as was done with Concealment would render stealth DPS a non factor in SWTOR, with Arenas already pointing in that direction.
The second paragraph makes me wonder whether you know much about the class or how guard works. You practically can't stay in stealth when guarding somebody, since guard transfers part of the damage. That mean you as the assassin tank take damage, and if a stealther takes damage he gets knocked out of stealth. And if you taunt somebody you get unstealthed as well. The only situation where assassin tanks really have a larger benefit from stealth is node guarding. Since for a tanking class they do a nice amount of damage, they are perfect not guards. But tanking a wz like a jugg could would be pointless, since for a tank you are too squishy in comparison.
The only stealth spec that can make use of stealth in open fire massively is the operative healer, without anyone doubting the OP PVP healing class. Despite the free instant emergency heals you can spam below 30% health combat stealth provide the "oh ****" CD, that can keep you and your team alive when you are focused. Playing this class I can ironically say the only class that really can reliably cause you massive troubles are dps assassins. Taming them down more, would actually make Operative healing even more overpowered :P
You and I are not communicating. I take the blame for not being clear. I am saying that a stealth tank is not viable without changes. My suggestion is if you want the to tank like a jug trade stealth for my base damage reduction.
I also agree shadow burst is where it should be but they don't need burst plus sustained DPS equal to a sentinel.