It's true that EQ's basic raid structure wasn't difficult. Every fight was a glorified "tank and spank" with a few extras thrown in for good measure.
AE's that damaged the entire raid was one of them.
Mobs self healing was another
Mobs without AE that just did crazy amounts of damage output was a 3rd.
If your group was exceptionally well coordinated and you could get a target into a good location to kill it while minimizing AE damage to everyone involved, that would be your best bet.
The other factor that came into play was just how quickly your guild was able to mobilize and take out a boss that spawned.
You needed to have adequate gear to survive an encounter, which means that to do high end, you had to farm lower end. And in many cases, servers like my own would continue to farm important lower end items, just to keep them out of the hands of a rival guild. Things like threat weapons for your tanks.
It gave us the edge and you couldn't really compete without them.
The Emperor fight in Ssra was probably my favorite. There were a lot of things going on there.
1.) Mobs that had to be mezzed
2.) Mobs that had to be off-tanked
3.) Raid required pecial weapons to do melee damage to the boss.
If 1 or 2 failed, the group wiped.
If 3 wasn't sufficient, raid would wipe due to 1 and 2 running out of mana.