Obviously diffraction is a negative function of smaller f/stops. But Depth of Field is a function as well. Depth of Field is an obvious matter that has always existed and must be taken into consideration when taking pictures. We either choose to have a subject sharp or we want to render it as "bokeh." Diffraction I think -- my opinion only -- is a largely overblown concern and plays far less of a role in taking pictures than it does in worrying about it.
Diffraction is a lens design and production issue and a function of optical science. It is what it is. If it is the sole determinant of a camera choice, that choice ignores newer focusing capabilities, better shadow and highlight detail retention and obviously, higher resolution.
My choice? I ignore it. BTW, for landscape photography, unsteady air and haze are FAR larger matters than diffraction.
If diffraction is the only concern -- you may want to explore returning to an 8x10 view camera. But before you do, check out the thread here elsewhere comparing the D800/800E to medium format cameras.
Thom is obviously more articulate than I will ever be -- but he is writing to be read and to earn money. I think he sometimes points out the red herring in an otherwise pristine pond just to do what he does.