I admit to not having seen KS in much, but she was astonishingly good in Clouds of Sils Maria (offbeat Olivier Assayas from 2014). Acted the wonderful Juliette Binoche off the screen, and won a César for Best Supporting Actress — I think the first time an American won.
The person I cannot watch without wanting to cut my own head off is Will Smith. He might be brilliant, admittedly, because I’ve never got past about two seconds of screen time featuring him.