I think Winogrand can easily "get a pass on it" because of the quality of his work. As we all know, the "Art World" is not a great arbiter of what is good art.
In all of this, I think there are a few points to be considered. First, as far as I know part of his process was to leave film unprocessed for a year or more before he looked at it, in order to remove emotional attachment, residual from the moment of capture, which could influence his experience of the image itself. That sounds like quite a bit of intentionality to me. So he left 3 years of shooting behind when he died. How many unpublished pages did Ralph Ellison leave behind? More than he ever published, surely. For a better example, how about Emily Dickinson? Would you rage against her, because she wrote hundreds of poems, not all of them great, and left it to others to sort it out?
Take Picasso. He probably made more awful paintings than anyone else, ever, because he made so many of them. I mean, there are a LOT of awful Picassos!!! Does that diminish his status? He signed all of them, so obviously he, too, is a failure in the "art world".
Plenty of artists, be they photographers or others, have editors who help them. William Shawn is a great example. Art is rarely a process of rugged individualism, and the best artists often have those who help them develop, edit, and display their art.
I'm sure that the Mr. Pierce, the demiurge(?) of this forum, can tell us stories of great picture editors. Winogrand may have been an extreme case, but another part of photography, aside from "editing" is being in the right place at the right time, and knowing what to do then and there. He obviously knew that–you can see it from his pictures. Arguing more than that, about knowing the life of the artist etc., is really irrelevant to the quality of the work. And by the way, biography a romantic requirement, not a modernist one.