As someone who's slowly been working on tanking myself, I've found it depends more on the player, than the class/job. I've seen DRG that constantly attack other than marked targets, and draw aggro if I'm not watching carefully. I was swearing (mentally) at BRDs for a while for drawing aggro, but I mostly got used to it and on top of things.

It seems to me that the reasons why MNK and DRG don't have the same problems is because they don't have the same strong ranged attacks as the other jobs, so they're not launching those to start off before closing in. Instead, they're coming in a second or so behind, and most tanks already have their aggro established by the time they arrive. An impatient member of a job with a strong ranged attack to start, though, can mess things up in a hurry.