Personally, Lucas's comment didn't surprise me at all. To the contrary, it confirmed the perception I had of Palpatine. All dictators believe they are doing good. They see their own actions through the twisted lens of narcissistic arrogance and complete suppression of cognitive dissonance. I love that in Star Wars, psychological realism trumps archetypes.

(“Your feeble skills are no match for the power of the Dark Side”), suggest to me that he believes evil is more powerful than good

To him, the dark side is good. As he says to Anakin, "good is a point of view", and his point of view is that it's the Jedi who are evil.