I don't know about Act I and II, but there's no way Kallig beats Act II or Prime Nox. The Force Ghosts empowering him and making him partially immortal give him the edge. I honestly doubt very few Sith [at least during his time] have the capabilities to withstand Thanaton's storm in the way he did/own the hell out of him afterwards.
And this might not mean much, but Khem Val does recognize Nox's power by the end, declaring him the "heir of Tulak Hord". My guess is Khem now views Nox as Tulak's equal, but that's just me.