As a tank, I am always happy when a DPS is doing their job. At the same, if I can't keep a mob off a DPS, then I'm not doing my job. There will be times where a mob WILL wander off, but it should easily be recovered. Playing casually, I can still keep mobs on me. The one thing I hated as NIN is when a mob comes for me from a simple Duality + Aoelian Edge (buffed).