Oh but it does. Because Revan, being a user of both the Light and Dark Side would be affected by the nexus on Droumund Kaas.
Ah, finally someone brings that up. Good.
You are making a false assumption here. He wields them both with raw, equal power. The Dark would be amped by the powers of Dromaund Kaas. Meanwhile, the Light would be tampered with and made weaker, as obvious. It would take, logically, the same as not being on a nexus, or even greater effort, to balance the two forces out. You do realize how incredibly difficult it is to balance it out even without being on a nexus? That is why like no one does it.
However, even ignoring this, his Dark powers would be amped the same as Nyriss' lightning, so it would equal out regardless. 😉 Try again.