Yeah, I don't see how a Grievous who could press Windu would get challenged by Scourge in a pure sabers context. Scourge holds no noticeable technical advantage over Grievous, who knew every form, having been personally instructed by Dooku, and was able to train magnaguards to an extent that his elite could challenge Shaak Ti, nor will his raw power overcome someone who could stand against Mace Windu or the elite of the Jedi Council. Grievous, meanwhile, has the simple advantage of being able to strike rapidly with four lightsabers; it was enough to press Obi Wan, the prototypical soresu master, let alone Scourge, who certainly has not demonstrated the defensive skill and hasn't really done anything beyond killing some dark council members off-screen.