Mate TBC was notorious for being the most unbalanced PvE scene in the history of WoW. Allow me to paint your picture: Minimum of 5 resto shamans, minimum of 8 warlocks. More than half the raid is already filled due to class-stacking. When the glaives come, all other DPS spots will be lost to glaive-rogues and the occasional glaive-war.
No it is in fact one of the worst when you take a closer look at it. Class-stacking in PvE and in PvP you will only see Sub-rogues, SL/SL locks, Frost Mages, Feral dudus and insane amount of Rdudus with a few disc/shadow priests. Warriors are useless on their own vs all other specs, you always need a pocket healer and a dispeller.
Oh please, M'uru was not hard, it just required all guilds to go "wtf is mandatory profession? Leatherworking" and fix drums for the entire raid. M'uru on its own is not hard, just requires some brain work and dispells. Not to mention the willpower to enjoy a fight in one of the most claustrophobic rooms in the game.