My guild had people practicing it before we started in work/school.
I don't think BT was that difficult personally, most of the first half of the instance was faceroll, Bloodboil could be hard, RoS was by far the hardest, and council and Illidan weren't really large cockblocks.
Tbh I think Vashj, Kael and Archimonde were the hardest encounters in TBC (not including sunwell). My guild certainly spent way longer on them than any other
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Oh God yes it still exists