Rears on mine are loaded (~1100lb total). Still need about 600lb on the 3 point to utilize full loader capacity in less than ideal, real world, rarely flat conditions.
3 point ballast has the advantage of transferring weight from the front axle to rear, which is arguably an advantage over wheel weights or liquid ballast for loader work. That may or may not be intuitive, but the physics of that has been beat to death in several other threads.
Wheel weights and liquid ballast are better for increased traction. (A 550lb box blade is decent counterweight for loader work but does nothing to increase traction when it’s on the ground cutting dirt.)
Liquid ballast adds much more weight than wheel weights and is less expensive. Your wheels may or may not have the option of weights. (Check the OM for your model for details.)
Liquid ballast is better at increasing stability due to having a COG lower than the axle in contrast to wheel weights which have COG at axle center. (A tractor tire “full” of liquid is ~75% liquid, 25% air by volume.)
Tractors the size of ours are multi-use machines that are relatively light weight unballasted. They have options to add front weight, liquid, implements or dead weight (ballast box) on rear. They’re intended to be ballasted appropriately for the tasks you have for it. For some, that’s no ballast at all.
Sounds like your uses require adding weight to the rear. If you finish mow with it or have some other task where you need it light at times, I would suggest a ballast box or some heavy implement you can put on the three point for loader work and remove for finish mowing, etc. If you don’t have a task which requires the rear to be light, I’d fill the rears, see how it performs, and add weight to the 3 point as needed.
YMMV.
Hopefully someone with your model will weigh in with specifics of rear ballast needed to utilize full capacity of the loader.