We don't know enough about the Exile to draw a fair conclusion. Yes, she killed three Sith Lords, but how did she kill them? Did her strength lie in tactics, raw Force ability, or lightsaber skill? Did she defeat Nihilus without exploiting his bond with Visas, or did she need to in order to win? Was she nearly killed by Darth Traya at the end, or were they on equal footing? We don't and can't know any of these things.
"Grant Allen [...] had written a book about the Evolution of the Idea of God. [...] it would be much more interesting if God wrote a book about the evolution of the idea of Grant Allen." ~ G. K. Chesterton, The Everlasting Man