Ok, so Vitiate might be able to subjugate Dooku under his will here, but in terms of combat, what has he got? He just seemed like this dark and nebulous point of convergence who could make bad things happen to other people. Now obviously his knowledge is on point, but the fact is, the confrontation with Revan, Meetra and Scourge scared him out of his wits, he obviously wasn't prepared for combat and took measures afterwards to ensure its resurgence wouldn't have such setbacks.