Lets clear up what this does.
Linear (F) vs progressive (P)
Linear is a 1:1 ratio, so if the "swing arm" moves 1" then then the shock moves an equal amount. ( not 1' ) If you broke down the movement of the rear shock into 4 1" movements you will always get the same movement at the shock shaft every inch.
Progressive is just that progressive. Rising rate or falling Rate
So if we move the swing arm 1' every additional inch we move the rear swing arm the shock shaft will not move relationally.
So the first inch of swing arm movement lets say the shock moves 1', then the next inch of swing arm travel it may move .5'. (2:1)
This is a bit tough for me to explain, hopefully that makes some since.
So how does this effect your bike in the real world.
If your going along and hit a bump with a passenger in flat ( F = Linear ) then your shock cannot move as much as you may need based on the spring.
If the same bump came along and your in progressive ratio then the shock is allowed to move more for the same swing arm deflection. Hence softening the ride.
A flat curve is always better in controled environments and properly setup for the bike load. However the motorcycle is sold and its anyone's guess what load it will be put under, by load I mean weight it has to carry. So a progressive ratio is best.
Regarding your concern, Ducati is worried the bike will get very upset if the swing arm is not dampened properly causing rider to loose control.
The rear spring is calculated for a 200lb rider, now what happens when you throw another 150 lbs or more at it, the spring can no longer work as expected so leverage must be used to accommodate the extra load.
