To answer the question of the OP, the actual first player to hit 60 was a Mage who basically did nothing but AoE-farm grind his last.. what was it, 10 levels? In EPL I believe. No layering abuse or anything.
A small portion of players probably abused the whole 10-man in dungeon thing. Normally, a raid group of players should completely kill XP gain. However, for whatever reason, raid groups in dungeon did not kill the XP, but instead added extra group bonus XP without cutting it further for 10 players, meaning that you basically doubled XP gain in a group of 10 compared to a group of 5, not even mentioning the greatly increased kill speeds possible.
Finally, as for killing Ragnaros, the most grindiest part of clearing MC is probably the quintessences. Note that you do a few quests OUTSIDE of MC, which give rep as well as requiring you to kill mobs that also give tidbits of rep to work your way up to the quest where you have to kill 4 bosses in MC - The 4 salamanders which were essentially killed in, what was it, 20, 30 seconds each?
Overall, a bit harder now, but NOT that hard. Dedicated players planned their entire leveling grind out, and those who wanted the dubious glory of Classic WFs probably planned out the raiding bits too. Note that Onyxia only lasted so long because the questline to unlock her lair is long as fuck.
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Blizz specifically mentioned that the bonus XP that you get from grouping up (Which, mind you, does NOT get split) behaved oddly in a dungeon group with 10 players rewarding more XP then intended, outside of the whole "No XP from raid" thing that it was supposed to be.