Totally understand and it’s annoying…lol
Quick test would be to run all the monitors at the same refresh rate and see if the mouse use has the same “feel” across all of them. Chances are the 2 other monitors run at a higher rate so when you get to the 4k it feels worse/sluggish.
I’ve had my 4k for a few years now and have done exhaustive tests in getting Cubase to feel smoother on a 4k. Truth is after all this time I’ve gotten used to the 30hz so I know when I get my next main monitor w/a higher rate it’s gonna feel much smoother.
Sad part is how it’s 2019 and it’s the first time Cubase acknowledges higher resolution.