She was more hateful in earlier episodes, but in order to keep some sort of freshness to the show and characters, they evolved over time. Houlihan in the movie had no redeeming qualities that I can remember, but TV's Houlihan became more complex from the middle seasons out with a lot of qualities to like.

Yes unlike Frank Burns who never changed, Margaret did grow as a person. I hated how she allowed Frank to browbeat a nurse and never defend them. Years later, I loved that scene with the nurses.

Actually Frank had some goodness scripted here and there. He and Margaret both get worried about the Korean lad in the minefield in a Season 2 ep.

That is true. Frank did have his moments like that one with the kid in the minefield.