His early work in 10 Commandments and Ben Hur should keep him from ever being in a "worst actor" category.
Those alone should keep good ole Charlie from ever being in an "actor" category. Didja ever see "Planet of the Apes"? He did his best work there while he couldn't talk.
But, see, "actors" from that era weren't really "actors." They were "stars" who were recognizable from the persona they projected onscreen. People would go to see 'em just to see 'em. It was a different world before Marlon Brando. There were so many of 'em: John Wayne, Charlton Heston, Kirk Douglas, Hank Fonda, Humphrey Bogart, Clark Gable, Cary Grant ... the list goes on and on.
Thing is, they weren't characters, they were personalities. They were kept in the movie studios' kennel and groomed to have enough universal appeal that any movie they were plugged into would make money because the public would come and see 'em no matter how lousy the vehicle.
Some tried to take their craft seriously. Others just wallowed in it. Evaluating them on the basis of their acting ability is kind of like evaluating spermatozoa on the basis of their swimming ability ... they're there, they're doing what they do, the outcome is whatever it is ... and I ain't evaluating the female side of things, which is a different kettle of fish altogether...
Put my faith in the people
And the people let me down.
So, I turned the other way,
And I carry on anyhow.