As someone who used to both k/m and controllers for RPGs [not shooters], K/M is almost always more accurate. I tested it in most from swift ware games that favour controllers, and platforms that favour K/M. In all instances K/M is better, even if you can get good and used to the controller. Here is why.
1) controller has huge lag with input. Even good controllers like my own have 0.5-1.5ms delay with a wire, wireless is going to be worse. My K/M has delay of 0.1ms. That is huge difference
2) mouse + KB makes macros possible, they can make huge chains of 20-30 keys done in one second. Best example is Ff14 and healing. Where you macro to target your ally with lowest hp and in one click can do your rotation. Good luck doing that with a controller in fast paced combat
3) Turning camera by simply moving your arm is more precise then flicking your controller
