A lot of the problem these big hitters face is that they rely on their favorite shot to end points quickly. In this case, it the Raonic FH. By the time the ball comes back a couple of times they are out of position.
Raonic really has a North American game - big serve, big FH, BH is a liability. That being said, to his credit, he still trains in Spain part-time and his coach is Galo Blanco. Unlike Americans, he's serious about improving his game on this surface.