I've never videotaped myself or others mowing before, so I don't know how I or others look while mowing.
I watched all of your videos...
That being said, your culprit is that when you bounce (or your lady), your bouncing your arms and jerking the sticks back and forth. This is then jerking the machine more and then your hit the next bump and jerking it back. If you were to ViseGrip the levers still (do NOT try this, but imagine it) your ride would be smoother.
I drove your exact machine on two separate occasions, about a year apart. Both demo periods were multiple day. Go back and search under my username. The first demo, it was brand new....never cut a blade of grass. It had standard forks and those same run-flats that all the new ones did.
My main complaint was the stiff riding run-flats.
The next season, I demo'd it again. This time the dealer installed a set of flex forks. It was a totally different machine. Rode great. Way better than my older rigid forked, air tired, flex seat XR-7 SuperZ.
I did notice the absence of the flex seat that I was so used to, but I was able to go faster and ride smoother with this new machine with flex forks.
Couple of things...
Both demo periods, the mowers came to me with 20psi in the rear tires (which may be what is posted on the sidewall of the tire). Both times I aired them down to 10psi, as 8-10 is the Hustler recommended pressure.
As for the deck bounce...
Hustler re-engineered the geometry of the lift mechanism on this new SuperZ. They lift a LOT easier then the older models did. This new deck is heavy, and to counter that they made the springs do a lot of the work. You look to be cutting low (under 3"). I would re-adjust the spring tension as at your lower cutting heights, the spring is almost FULLY compressed and giving you almost all it's upward pushing power. Loosen them up to where your comfortable with the leg pressure needed and the bounce to almost go away.
And lastly... slow down! Or get some smoother lawns. I'd bet that if your other mowers could do 15mph, that you'd ride just as rough!
Any other mower with similar wheelbase and 1.5"x3" frame rails will ride exactly the same. Your rear suspension is your rear tires after all.
2004 GMC 2500HD Reg Cab BOSS 9.2 V-Plow
2013 eXmark LazerZ X-Series 60" 34hp EFI (RED) Kohler
2006 Hustler SuperZ 28EFI 60" Power Chute Design OCDC SOLD!
1996 48" SCAG Belt WB 14hp Kawasaki Classic Deck
Echo 2 strokes PB-755
Commercial Lawnboy trim mower
Solo since 1980