The surface suits his game fine; his breakthrough was here 2 years ago, getting to round 4. It's more that his form has been awful since he lost the Tokyo final to Nishikori last fall.
But a big server is always dangerous. If you can't break him, it comes down to a point or two in the TB. Or you get frustrated and get broken yourself, and there goes the set.
Fair enough. I just think his game is better suited for faster surfaces. The slower surface takes pressure off when facing Raonic in those point or two moments you talk about. It just gives the opponent that little more time. Maybe the get a racquet on a big serve or to run an approach down. I'd be more worried if Roger faced him at Wimby or the USO.