Raise your hand if you replaced your Planar armor with the various pieces of Tolan's/Donal's/Deepwater/Mrylokar etc. armor in Kunark. You were replacing raid gear with single group gear. Yes, two pieces did come from raid targets, but the point stands - base AC value & added effects made the armor more desirable.
In Velious, though there was no level cap increase, single group players could get armor better than the Kunark raid set via Kael & dwarven armor quests.
Offhand, I'd guess that high level (67+) blues in TBC will be of roughly the same power as T2ish armor, though probably not exactly the same, and the level 70 stuff will be comparable, but maybe slightly worse than T3. But that's just an initial guess. I haven't played since Feb '05, so I'm not going to claim omnipotence here.
