They are of a different time, and type of comedy.
For me Jerry Lewis is really amazing, but his films do not hold up. I think I have seen his biggest half dozen or so films, and I would only begrudgingly watch them again.
Now that is not to say he was not fantastic, but his performance is the only thing that makes those films compelling at all.
Looking at Robin Williams. A lot of his comedy films are really good films, and Williams elevates them. So you at least have a decent film as a basis, that translates to modern comedy enough that they do not feel super dated.
Jerry Lewis films feel a bit more like Mr Bean, or later Eddie Murphy. Where the performance is fun, but everything from the direction to writing is shit.
So Robin Williams destroys Lewis just based on the quality of the material.
Looking at Charlie Chaplin, is a more interesting comparison. He made classic films that are both fantastic because of his performance, but he often did it without any real dialogue.
Not to dismiss Jerry in the end. But his films were mostly shit outside of his contribution. And even with his contribution, they are still not films I would revisit.