No, I never think of a performance in terms of "supporting" or "leading" - just in terms of good or not, and Kidman is not.
Copy that. Disagree.
As for End of the Affair, again, RE-rewatch. She's very good.
Julianne Moore isn't bad but I don't think she quite conveys the inner-life and turmoil of Sarah Miles. I like her quite a bit. Apparently Kristen Scott Thomas and Miranda Richardson were both considered and I think they would make much stronger choices. She's a bit wooden opposite Ralph Fiennes whose passion seems ill-aimed.