You could easily tell the difference between a gladiator and a random 2k mage because the gladiator would bait out the cs and wand twice to delay the eventual poly. Good rogues would weapon swapping deadly poison as sub to protect wound from poison cleansing totem. Getting hard casts off were rewarding and realistic to do so, instants were mana inefficient(huge risk/reward) and could not create/alleviate pressure by itself.
Juking priest fears, warrior/hunter deadzone kiting, jumping roots,strafing cone of cold. Low amounts of mobility cds across all classes using them requires a lot of thought process and coordination.
There were terrible imbalances in tbc and wotlk but that was only an issue of numbers. Flat ARP was too strong, damage was too high for certain classes; If the numbers were tweaked it would have been a good game. Even if all the numbers are balanced now the game is terrible from a design standpoint.