I have sold off most of my Dagor type lenses so mostly agree with your comments. Modern plasmat type lenses are sharper at large apertures than Dagors, and probably have better coating.
However, the design itself did not reach the end of the line in the 1970s with the multi-coated Kern dagors, which are some of the most contrasty lenses ever made. The fairly recent Schneider 550mm XXL Fine Art lens is in fact a true Dagor design which takes advantage of new glasses and computer design. So with all the background of lens design Schneider chose a Dagor type design as the one that best delivered the specific image qualities they thought important in a lens of this type.