Hopkin’s performance in The Road to Wellville was comedic in nature and he wasw great in it. So he is definitely capable of comedy.
I’ve read that Stanley Kubrick kinda tricked Scott into giving that performance. He asked him to play the role really broadly for a few practice takes, with the promise that he wouldn’t use them, and then he did. Scott was not amused.
I’ve read the same. I think the best directors (like Kubrick) follow their own instincts rather than cater to the whims of their actors. Kubrick may, for example, have pushed Shelley Duvall too far in The Shining (she apparently suffered nervous exhaustion from the many takes he pushed her to do), but he got a stellar performance out of her. Stanley was a perfectionist, and that’s what it takes to make great art.