Revan was not easily manipulated, or manipulated at all. He and Malak were both unprepared for Vitiate's mental dominance after they were betrayed by one of the guard. Vitiate dominated their unshielded minds and send them back to gather intel. However, Revan's mind and will were too strong and he broke free of the domination, instead just turning to the Dark Side and becoming Darth Revan where he then set about building his own Empire and, given the vast knowledge he collected about the Rakata and the Star Forges, if that moron Malak hadn't turned on him, Revan would've conquered the Republic and then taken on the Sith Empire.

Let's see, before all that, the Jedi Council told Revan not to get involved with the Mandalorian War. So what'd he do? Formed a movement within the Jedi Order and Got Involved. The only time people seem to believe Revan is "manipulated" is after he's gone through Extreme Mind Screwing. First at the hands of Vitiate who is essentially one of the most powerful Dark Force users ever conceived, and then later when it took the Entire Jedi Council to wipe his memories and impose a new personality, something that didn't stick as Revan's memories started coming back a year after he was released.

You wanna talk about being manipulated? Anakin/Vader has been being manipulated since he was 10yrs old! There is No denying this. It's a stated fact.