The two are not mutually exclusive.
To detect whether continuous tones were being sacrificed, I would expect that a good indication of such might be presence of banding* in photographs of subjects having significant areas of non-textured continuous tones. There are continuous tone charts that might be useful for actual testing of the lens design hypothesis. Alternatively, a contact print of a rectangular graduated ND filter might suffice. Once generated, such a test subject would be photographed to analog film with numeric evaluation done by densitometry, though any significant banding might be readily observable by direct examination with loupe on a light table.
Of course, there is a competing hypothesis that some lenses are intentionally softer with the intent of generating continuous tones where the subject actually has an abrupt step.
Steve
* One might also expect interference patterns as well with digital capture.
Last edited by stevebrot; 07-15-2019 at 05:49 PM.
Reason: completeness