That is exactally how I tow mine. What is wrong with that? The brush guard is held on with like 6 large bolts directly to the frame. It isnt going anywhere. And there isnt much choice on the rear other than the drawbar. Wrapping the axle, there is too much wiring and small linkages (3PH feedback, 4wd, etc) that could be easily damaged.
My advice is legal no matter the weight. Once you get to 10K LBS as I recall you must use 4 points and all I listed. Also keep in mind rules are open to interpretation by a LEO should you get stopped. I sold a Deere 850 compact tractor a few years ago. The guy that bought it hired a contractor close to him to truck it to his home. I helped the contractor load and strap the tractor. While we were doing this he told me he had a Deere 755 and was ticketed for doing what you describe. He had a chain through a clevis and the strap from one side to the other dropped over the base of his brush guard. While below the weight limit (like I said I believe it's 10K lbs)s, the ticket was just for improper securing the load. It did not give a model of the tractor or any weight. There was no way this guy could prove the tractor he was ticketed for, was the tractor he was ticketed for. Since then he said he strapped everything as I described
Also keep in mind this is general information, brush guards come in all shapes and sizes. Not all could or would hold up to being tied down. The clevis through the drawbar with a single chain while not legal above a certain weight. It would give a very low angle on the chain. I have always been told to try and keep the angle between 30 and 45 degrees. Anything over the size of an ATV, my dad, my cousin, both who have CDL's and moved all kind of construction equipment, and I. We all treat it like its a large machine, 4 points plus one over each attachment. It's just a lot less trouble that way. In NY you are just a likely to get pulled over now in some areas with an F-150 as a big rig.