The seedlings of Duke are remarkably uniform, with vigorous growth but tight internodes. I can see why so many of its seedlings have been selected to be clonally propagated. I think most people would find most Duke seedlings to be just as satisfactory of a rootstock as those UC selections.
To give an example of what I mean, here was the “seedling class” of last year in October, with the Duke seedlings circled:
They look almost like clones! Far less variation than among the seedlings of other cultivars. For those curious about the other seedlings, here was the original caption when I first posted that photo: