I don't play tank but i usually don't have any trouble with targeting. I play SCH and DRG.

Play with PS3 controller on emulater.
To cycle through mobs i hold down R2 (button that pulls up my right macro pallet) or L2 and tap R1 or L1 to cycle left or right. This targets only enemies.

just something to try because i use it and can change targets fast and efficiently with it.