Without gainsaying your choices, I will say that I don't think I've ever seen a Christopher Plummer performance that didn't feel wholly authentic.

In addition to your (well chosen) list of fine performances let me add the following:

--I especially liked one of his last performances in 'Knives Out,' as an aging mystery writer who (spoiler alert) from beyond the grave, thwarts his feckless descendants in order to reward the one honest person in his life...

--I don't think 'Inside Man' would be one fourth the movie it turned out to be if Plummer hadn't played the fulcrum upon which much of the plot (it turns out, spoiler alert, again) hinges.

--My all-time favorite Plummer movie turns out to be my all-time favorite Sean Connery film (reportedly Connery's favorite also....), my all-time favorite Michael Caine movie and tied (with 'The Dead') for my all-time favorite John Huston film: 'The Man Who Would Be King.' IF you haven't seen it, go, now and do so... Else you should not call yourself a real (reel?) fan of cinema...