Not hard at all. MC was already considered very easy at the time, a time were many people had no experience of the game, little experience of playing, flasking was unheard of (it only became a thing later in the game, and only for competitive guilds) and gearing was all over the place.
Even then, it was piss easy. The first time our guild played in MC, we were only 25 people (the hardest part of MC always was to bring enough bodies) and we killed the first three boss. A number of us had experience (they partnered with another guild to help them fill their raid while most of our guild was leveling and getting dungeon gear) so it wasn't the "surprise, motherfucker" that you'd see on many first-timer that were slaughtered by the first giants, but we still killed several boss while being at basically half-strength, and half of us having a mix of blue and green.
MC was tuned for inexperienced people in leveling gear. Being in full blue was good enough to be considered a good catch for a pick-up raid. With the mindset of "let's optimize" that many people got nowadays and the obsession of "BiS", you'll end up with people that functionally outgear the content, while already knowing the tactics and having years of experience under their belt.
People from current WoW will get a few nasty surprises due to the bad habits they got there, but once they adjust, MC is going to be facerolled hard.