Some people may not know that the old tier sets, as well as the bosses that yield them, still exist. On my original priest that was long since traded away or deleted or both, I had EVERY single piece of Transcendence gear, and I got that gear at a time when resilience did not yet exist and there were no higher instances in the game than Blackwing Lair. I was literally the best geared priest on my original server, Smolderthorn, for quite some time.
Unfortunately, that character was deleted from WoW years ago, and my new priest, of the same name, has fine gear but not the legacy pieces that once stayed in my bank.
HOWEVER, you can still get this stuff! I am now going through the process of clearing Blackwing Lair ALONE! Despite many naysayers online, I successfully destroyed the first boss, Razorgore, using Discipline.
I got about 60% of the eggs on the first MC, and he was still above 80% health. It took 3 MCs total, and he had about 40% health left at the last egg. He is, of course, simple to kill at that point. The only trick is not getting him killed during the egg hatching, but the adds seemed to favor me, for whatever reason.
Good luck all you priests! And stay tuned as I continue in BWL on my quest for the lost tier 2 gear. Btw, nothing dropped from Razorgore, so I'll have to try him again next week. Also btw, I had to get attuned to BWL, which was a simple process that involved soloing upper Blackrock Spire (UBRS), which was a lot of fun to see again as a level 90. All in all, it took 5 attempts to learn his fight, but it took almost just as long to find the entrance to BWL. When was the last time you entered Burning Steppes anyways?