I would have taken ‘non controversial’ to mean someone who was moderate or middle-of-the-road. Someone who tried to compromise rather than defeat their rivals/enemies. Previous Tory Leaders had tried to reach a consensus (at least within their own party) Thatcher did not, she was a polariser. The term ‘controversial’ fits her any way you put it, and I admire most of what she did....
Every politician tries to defeat his/her enemies. The only question is whom the said politician sees as enemies.