For me the black frame isn't that important, this was to say that a cropped picture makes it more difficult to guess the focal length it was taken with because it kinda modifies the perspective perception (sort of).
Two years ago I went and visited the large HCB retrospective at the Centre Pompidou in Paris :
[Nikon S2, Nikkor-H-C 50/2, not cropped
😉]
And - to my great surprise - none of the photos were displayed with the legendary black frame ! Clément Chéroux, the exhibition curator, told that this was his own choice, because he was finding this black frame thing a bit questionable at the end of the day.
That doesn't mean I don't think HCB was a genious. He was.
😉