Initially, yes. K+M does provide an accuracy bonus. However, after meaningful practice, you can match that bonus with a controller, as you have gotten accustomed to the mechanics of the game and the controller, to the point where it does not really matter which tool you use.
It's not just an accuracy bonus, it's a speed bonus as well. With enough practice, you can almost instantly get your crosshair pretty much anywhere on the screen. However of course, if you turn up the speed on your controller you can do that as well. However, comparatively, it's much harder to do on a console accurately.
Let's model this difficulty with some math equations. The equations here will be of the form (a + 1 * x) / (x + 1)
Basically this graph will represent how close to fully mastering the game you are, with 0 being incredibly crappy to 1 being you'll never be beaten by anyone ever.
a represents the initial amount of advantage that the control method gives. As x gets higher and higher it will get ever closer to 1. And, theoretically, if you could practice infinitely, for any given value of a you'd reach one.
Let's say the keyboard+mouse gives an initial advantage of 0.5 and the controller an initial advantage of 0.
The upper line is the keyboard+mouse, and the lower one is controller. Now, no matter how far along you go on the graph, there will
always be a gap between the two lines. This can be proven as follows. Let's say there was a point at which the two graphs intersect, that would satisfy the equation (x + 0.5) / (x + 1) = (x + 0) / (x + 1)
Multiply both sides by (x + 1) and you get x + 0.5 = x + 0. These line graphs are parallel. They will never intersect.
THEREFORE. No matter how much you practice on controller, as long as the people on PC practice just as much, you will never be better than them, no matter how small the difference.
(Sidenote: As long as the value of
a for keyboard+mouse is higher than the value of
a for controller, this holds true.)
