I don't think it's cheating. I play a lot of FPS on PC so it doesn't seem like a big deal (I'm learning to use a controller and it's just lucky I haven't chucked the stupid thing out the window some days.). I have heard people say that KB + M users have an advantage but I don't know. A lot of people are great with controllers and just dominate no matter what but on the other hand, keyboards allow for more finesse and control. For using a keyboard and mouse, the Youtuber's reaction times could be better, he doesn't seem to have the degree of situational awareness that he should have.