My old guild has existed in some form or another pretty much since Vanilla, we were something like top 40 to kill KT 40 back then. The Classic version of the guild had trouble getting through Heigan night 1. Was interesting to listen to those who had played Wrath Naxx and never experienced getting teleported into the eyestalk room which for whatever reason they didn't keep from Naxx 40 to Wrath version. Also just struggles to do the dance in general.
Not surprised in the slightest guilds cleared it in one night, though. With enough prep can figure out how to beat Sapph without all the frozen rune frost resist, and have always noted the whole "need 8 tanks with 4/8 bonus for 4H" was a crutch. Crazy to hear stuff about raids stacking 8 fury warriors, though. We had at least 3 good ones back in the day. Everyone has probably been farming all the world buffs and mats they need for awhile. Good shit, though.