I wouldn't say that. Kevin plays his role really well and knows how to move about the pitch, but Davies also makes good darting runs and links up play very well for his age. I will say that Mirallas provides much more goal threat with the ball at his feet, but Koeman has shown that he likes to have players that can press the issue and win the ball. If you move Gana up the pitch, it allows you to do exactly that. It is something I had to see in action before I called it ineffective, and Koeman likes to experiment.