...I have the exact same tools at protecting my allies as ST minus the accuracy debuff...
No, you don't. You're also lacking:
5% damage debuff (for 15 sec)
Ion Cylinder damage proc and movement debuff
Damage mitigation via shields...doesn't affect much in PvP, but it does help
Most likely reduced HP compared to a full spec tank
Any derp can toss around taunts, so that's a wash. The only benefit you're gaining by switching cylinders is being able to use Guard. You'd benefit your team more by not doing it at all and just sticking with DPS. Stance/cylinder dancing isn't very productive for any class.
Don't underestimate survivability. After a zerg by the opposing team, and the dust has settled, I'm always
the last one standing. I can withstand focus fire from 3-4 attackers long enough for reinforcements to arrive. I often get "unbeatable" and even "immortal". With even a semi-competent healer at my back, you and your team might as well forget it. You're not going to kill me, ever.