All good points, but I keep going back to the initial concern about tire repairs. My brother and I have experience with all forms of ballast and have plugged endless numbers of tires, my brother began his professional career as a tractor mechanic at the age of seventeen. When we began clearing our farm, we had to put tire sealant in everything that went in our woods or we were plugging thorns several times a day. For our uses, fluid in the tires simply did not work.
We now have about nine tractors and a backhoe and use combinations of fluid, nothing, cast centers, weights and combinations. We no longer have the thorns, but if we did, we would go back to what worked for us best initially which was not fluid filled tires and sealant, great now, but not so much otherwise. I can't think of anything more unstable on a slope than a flat.