. . . I wouldn't expect any reviewer of the day would have gone through the supporting cast noting their theatrical stage credentials.
Few mainstream reviewers would have, yes, but I think the more significant point here and now with respect to reception is that there was a particular set of racial attitudes within which such assumptions were made about supposedly untrained black actors and their "natural" or "instinctive" talent for dance, rhythm, and certain other forms of expression. I think most readers today would not understand what the term "native quality" meant, but I believe it would have communicated effectively 50 years ago with respect to this same general body of racialized attitudes, specifically in light of the film's exotic setting. This is not to say "we" have overcome all such views now, but it's now a far different and more complex picture.
Also, I think the benefits that Black Orpheus gave Brazil in terms of enduring international musical exposure outweigh any perceived negatives 50 years on. Global respect for Brazilian music (and consequently Brazilian culture) came hard and fast on the heels of this film.
I guess I personally don't think about it in terms of a balance upon which some things "outweigh" others, but I generally agree about the film's cultural impact. It was far from a void beforehand, with the Good Neighbor Policy, for example, spurring a lot of cultural interest in Brazil in the 1940s and '50s, and there were many collaborative projects involving Brazilian musicians such as Laurindo Almeida prior to Black Orpheus. But again, this is not to diminish the huge impact of the film around the world.