Gandalf Vs. The Witch King

There is no proof the added demonic force would have made the Witch King the equal of Gandalf the White. I have read posts saying the upgraded Witch King was now much more powerful than before - was he? Where does it say in any text that the extra force made him so? Wasn't he still much weaker than when Sauron last had the Ring, & Gandalf at the height of his power? None of it seems to make sense - we have a weakened Sauron who upgrades a weakened Witch King to the same level as Gandalf? All that without the Ring? Not possible. So when the Witch King dies, Sauron becomes weaker again due to the wonderful demonic force of his vanishing into thin air?

I agree with the above post in that the Witch King may not have known the true nature of Gandalf. Calling a balrog slayer an old fool!