My friend, your problem is coming from a washboard property in this video, believe me this is not rocket science, anyone looking (as Mick did) at the mowers movement knows this property is extremely rough. The washboard affect would not come into play as much if the peaks and valleys were not so close together. Mow up and down (parallel) to the ridges your mower is bouncing across, and it will be totally different. When you watch the mower and see that the flex forks do not have time to activate properly because of the high and low places being so close together. This means no ztr will ride good in that scenario, a fully independent suspension such as the one Ferris uses will by far give the best ride in a situation of that type, but nothing will be great.
Go into my post and find where I used a new IS3100 Ferris and compared it against my Super Z with the flex forks and flex seat. You will see where I talked about the washboard affect, such as you have in the video, and how the fully independent Ferris suspension does make a difference in this type situation.
I own and operate a new 35/72 Super Z, and have one area I could make the mower do the same as yours in the video, so what that means to me is I know I must slow down for the mower and flex forks to operate as designed.
I honestly can't believe you have not figured this out, and yes, I run both my Super Z mowers at full stick the largest majority of the time I'm cutting grass, but there are places such as in this video where I must slow down.