Good points. But you might go a bit further and say that all the "geniuses" had their poor designs.
As to losing interest, Newey has been saying for years that he'd like to design yachts; Gordon Murray turned to advanced road cars; Barnard moved to motorcycles and furniture; Mike Pilbeam went from pretty good F1 designs to better hillclimbers. I think there does come a point where there is a loss of interest or simple burnout.