I don't even understand that label, he's not even that great defensively unlike Simon who really is a pusher in the truest sense of the word. Goffin plays a lot like Nishikori but his strokes are similar to Simon's that's where the comparison ends. MWW says he's a cross between Nishikori and Ferrer/Simon and I agree with that assessment. He has excellent shotmaking abilities and if he had more conviction, he'd score more wins again the top 10.
I don't think he's a defensive player naturally like either Ferrer or Simon. Goffin is always trying to create angles and go for his shots - he can surely hit flat and deep with speed when he takes the ball early though his lack of height and natural power (though he has timing) makes him push the opponent back with top-spins before he opens the court for his shots. But he does NOT rely on the opponents UEs to win his points though he's varied enough in ability to occasionally try that strategy against players who are uncomfortable with grinding (like Raonic) but it won't work against Simon/Ferrer.
Having said that, today we did see some great defense (
) in the second set - but if it comes down to a pushfest, I give Simon the edge tomorrow. Goffin will have to think more creatively against Gilles. I think his gift is in his timing of his ground strokes that adds to his variety and his On-Court IQ that lets him study the match and try new gameplans if one strategy is not working. But his defense is not even close to Nishikori's. Nishikori's return game is superlative, Goff is still developing that.