The stiff sole helps the muscles in the leg, and that doesn't have very much to do with the tissue in the bottom of the foot. Replacement insoles are for addressing each person's particular foot shape; they don't make the shoe more floppy (my Specialized Tahos were floppier than either of my Sidis and gave me hot spots after 30-40 miles if I used small pedals; the floppiest shoes I've ridden in yet are my Nike Free running shoes).