I knew someone would bring up Totems.
In TBC, most classes had dramatically less abilities than they do today. Shamans and Hunters (with both Melee and Ranged) are probably the exception. For casters, downcasting was used more in PvE than PvP.
We could go class by class, but I think you'll find that most classes have a lot lot keybinds than they did back in TBC. Nobody says that TBC was easy mode because a Rogue had eight less abilities than they do now, now maybe there were balance issues, but the game wasn't any worse because of it.