Barel Ovair isn't a no-name. He was powerful enough to Conceal his dark side affiliation from the entire Order and could stand in the Council Chamber undetected. He was also clearly better than Eison Gynt, who was the most skilled Jedi in generations or something. That said, he was getting beaten by the Massassi even with Gynt's aid, while Sadow would've busted an army of the intelligent ones, which busted an army of the brutes that were beating Ovair and Gynt. That, and Ovair was driven half-insane just by being in the Tomb of Naga Sadow for an extended period of time.
Also, the nature of Sadow's possession there seems murky. Gnost-Dural describes it as Eison Gynt with "borrowed powers", which is a pretty strange description if you're taking over somebody completely.