strongbull saidDumont was a professional comedic actress. You should read the wiki page on her for a quick overview of her career. She understood the humor very well.
I think it was Groucho who said that Dumont didn't understand the nature of their movies' comedy, but then he wasn't always the most reliable source on a lot of things.
I notice you wrote comedic "actress" rather than comedienne. Another one who had a similar reputation was Lucille Ball, and we all know how priceless her I Love Lucy
Many of the show's writers and other staff agreed that at the first script reading for each new weekly show Lucille didn't know where the jokes were, and how to interpret them. It took the director, and often her husband and show producer Desi Arnaz, to guide her into making it funny.
Because she wasn't a naturally funny person, not like a stand-up comic. She had to handle it as an actress, a role she took on, leading one-time show guest Orson Wells to remark that she was one of the best actors
he'd ever met. But once she got her teeth into a Lucy script she made you believe she was the funniest woman on Earth. That is indeed acting.
Back to Dumont, I could believe she was far more clever than Groucho said, or whoever it was made that comment. Certainly she was the perfect comic foil for him: straight, solemn & severe played against his anarchistic craziness and wisecracking mouth. I don't think their scenes would have worked as well if she had been directed to try to mimic his lunatic behavior.