Some people are dumb and don't know their roles. If they're running ahead and aggroing everything, they aren't letting you tank and, yes, it can be incredibly hard to get a mob back once someone else has been attacking it first. Even in higher level dungeons, it can take me half the fight using Flash and Overdrive to get something back on me. Sometimes the entire fight goes by, I'm all out of TP, and all I can do is just try to keep it stunned to do less damage to the healer or whoever decided to tank.

You can have all of your gear and levels and skills up, and this situation can still happen to you. Some people just don't know how to play.