About the Sith'ari thing, and how powerful Revan is? Yes. About who would win in a fight between Revan and Nihilus? No. I don't see how Revan could beat Nihilus.
Revan is a militray tactican. It is unknown how good a general he is, but he is responsible for winning Malachor V, so he might be somewhat good, using deception to win.
Therefore, the only way I could see Revan winning against Nihlius is by finding the Exile and using her to defeat Nihlius, and then taking credit for the victory. In other words, by "cheating".