I used to play WoW at a relatively high level (no server firsts or anything, but end game raiding). I didn't always have the "best" UI add-ons installed and did some things that were considered beginner mistakes (keyboard turning), but I knew what I was doing and I knew the game well so I still performed well.

I actually had a good reason for keyboard turning, for those familiar with the game. I was a healer and used Healbot to let me click on player names to cast healing spells. Thus, I preferred to have my mouse free for this and used the keyboard for turning, which was minimal.