"Wait for 3 Sunders" It's a meme for a reason. Waiting for a tank initialize threat is boring/wastes time.
Mitigation damage and positioning the boss is the core of tanking. Even the tank not currently holding threat can drop mitigation on the other tank to help.
Regarding comments about good vs bad tanks, this weekend I joined an Ex party that included a note about using Provoke and Shirk. So some people apparently are missing the knowledge of proper tank swapping.