Steel would be great if the tractor had heavy enough weights. My jd for instance claims you can only add 2- 95lb weights per wheel. 380lb doesn't make a rats behind of difference to that tractor. Heck I weigh 230 lbs and I sure don't think it makes much of a difference in traction . Now the beet juice in the tires adds 800lbs+ iirc to each tire. That makes a big difference. The 1700lb counter weight is even better when it's hanging on out back. So steel is nice, but it's not the end all be all.
With all if that, I'm considering finding some steel plates to add to the inside of the rim....