I agree and in the case of the 575 I sold, it is at least 2 times as big as any in your pictures. It all has to do with safe and comfortable operation. You can run anything with anything but is it safe and efficient. I don't believe so. Don't see any full size round bailers either....
All flatland pictures as well.
You can make idiot squares with even a lawn tractor that has a 6 spline 540 pto if you want to. Nice thing about square bailers, even with kickers is, they don't need any hydraulic connections and the kickers have self contained hydraulics, independent of a tractor. Now my 575 required auxiliary hydraulics but just for the hydraulic cylinder the swung the tongue.