To the average player, no, it won't make a massive difference. But M+KB average is still slightly better than controller average. When you start getting in the Masters and GM ranks in Overwatch on console, you do start seeing more obvious KB+M players pop up. But that's because there are fewer players at the top. Plenty of average players using KB+M adapters in the lower ranks as well.

I've been using a XIM for years now to play with my console friends who I can't convince to go PC. Im average with a controller on most games, and far above average with the XIM. I've also been using KB-M since I was a kid. I don't think most people who've used controllers their whole lives would have the same immediate results if they switched.

That's a long winded way of saying, yes, it is a far superior control scheme and it will improve your FPS-stats if your only weakness with a controller is aiming. It's not going to do much for people who lack special awareness, game/court sense and all the other "skills" needed in an FPS game.