Getting some weight (implement and/or ballast) on the rear should help a good bit. I also found the dealer set the loaded R4 rears on my L at 30PSI. Dropped them to 12 and that greatly improved both ride and traction.
I would agree it takes some getting used to. Mine is the first and only HST I’ve driven for more than a few minutes. I tried a variety of foot positions depending on how much direction change was going on. The tractor bounce jouncing the operator bumping the pedal causing more bounce cycle; I’m familiar with from my early hours with it. After a few long days shortly after we got it rehabbing our private road and driveways with the loader, box scrape, and back blade, I couldn’t tell you where exactly I put my foot or how I avoid the bounce, jerk cycle. All I can tell you is now it goes the direction I want at the speed (within reason) I want like it’s another appendage. That’s why it might be worth considering giving yourself a few hours in the seat before you start making mods.