"Yes-sayers", did guild members today grow a boss killing glands or raid completing appendages? WTF?
Mechanic of the game didn't change that much for those years and there's a limit of hurdles on WoW you need to train to overcome. At some point you've just trained to the max, have all available theorycrafting (and by end of BC you DID have it already) and all you need past this point is time and math/RNG blessing behind your strategy. With exactly previous tuning, current guilds would take exactly previous time to complete content.