I think Ma Kawasaki put in soft, dual rate springs to compensate for the damper rod's harsh compression damping.
Sticking in stiffer springs, either constant rate or 'Progressive', may reduce brake dive, but it will make the overall ride harshness worse, because what you feel when going over a bump is the sum of the spring compression force and the compression damping force.
The way that makes sense for me is cartridge emulators, for compression damping that's less harsh, coupled with stiffer springs to better control wheel motion and dive. In fact, I installed emulators first retaining stock springs, looking for increased comfort. Only later did I replace with 1.0 kg/mm Racetech springs for better road holding in bumpy turns.