In all honesty, Revan is more powerful then Darth Vader. This shouldn't be a debate.
And it is really foolish to assume that Revan performed poorly against an Imperial Guard individual; Revan attempted to overwhelm him with his Force powers but Valkorion had significantly bolstered Imperial Guard's defenses via Sith Sorcery. Revan then switched to melee combat and outdueled his opponent in just two moves.
Now, an Imperial Guard individual is on par with a Jedi in single combat. So Revan logically outdueled a Jedi-level opponent in just 2 moves. How the hell is this poor showing?