Endgame is super easy, if people know what to do and are doing their parts. Running UBRS with a team that doesn't communicate or do their stuff properly is a nightmare.
Onyxia was never hard. Neither was MC. They are both entry level raids. It's not them people talk about when they talk about difficult things in Vanilla. The only challenge in MC is Ragnaros, who actually requires some DPS and gearing up for and consumables.