Tanks had to pull, because typically, whoever hit the target first would have aggro for the duration of at least the tanks first full enmity combo if they didn't have provoke up or wanted to save it.

Nowadays, taking aggro back as a tank is as easy as hitting the enemy once.

As a DPS with a timer mechanic, you'd just have to eat the penalty and start your rotation again, now you don't have to, now that the tank can claim aggro back in a flash.

Of course if the tank hasn't pulled because they're not ready yet and potentially afk... you'll have screwed up.