I think it's not about how fast they could do it, it's about why they'd care. Method raiding guild, not the affiliated streamers, are all about beating new mechanics and discovering boss encounters, being on edge while having the most optimized setup ever. Classic has no new mechanics to beat, no boss to discover and while stacking rogues and warriors could definitely cross the optimization box, I don't think they're interested at all about, we all agree quite fun, but technically outdated content.
Right now most Method raiders farm the hell out of Azerite, optimize their different characters and are vivid about 8.2's raiding. And while some Method affiliate streamers definitely will grind the shit out of Classic like Ziqo and Venruki, they're dedicated PvP players, I don't think they're interested at all about beating PvE content before everyone else. And Djarii is all about boob painting, unless you're interested about Ragnaros having tits there's so much "competitive Method" you'll ever get in Classic.