To take the discussion or analysis a bit further each of the different Hp ratings of the JD 50XXE series comes with a different tire size to maximize the ability of the tractor to transmit the power available to the ground as tractive force. My 5045E came with 13.6 x 28 rears. If I had ordered a 5075E it would have come with 16.9x 28 R3s.
So power to weight has little value you say? If you are out pulling a big implement through the dirt it is the only thing that has value.
I think matching tire size to the machine/power is a good idea, but you're using the power to weight ratio backwards, or at least describing it that way.
You were showing how the smaller machines listed have 6-70lbs per horsepower, while your Deere has over 110lbs per horsepower and suggesting that it's a good thing (not arguing that).
That means you have a lower power to weight ratio. 45hp to 5000lbs (ballpark) = .009hp per pound.
Something like the Kioti CK35 is 35hp to 3100lbs = 011hp per pound.
If power to weight is so important, how can it be that the smaller tractors can't do as much as your 5045 even though they have better power to weight ratios?
Weight is one thing, traction is another, power to weight ratio is another, and load pulling ability (like the old drawbar tests) is yet another.
It's pretty obvious that your 5045 would pull a much larger implement through the dirt than the CK35 even though it has a lower power to weight ratio, so there must be a lot more to the equation.
Power to weight matters most when you're talking about acceleration, which isn't what we really do with tractors. You want a lot of weight to get good traction, and then enough power to take advantage of that traction, but more often than not we run out of traction before power.
To keep it apples-to-apples, if we look at the same machine with different horsepower levels, power to weight starts to mean something....a 5075E can do more than your 5045E, but they have the same weight, and basic size to work with so it's a pretty direct relationship. Once you try comparing to a much smaller/larger machine, with significantly different weight, power to weight loses meaning since all the other variables get changed. That's why I said comparing CUTs to Utility machines doesn't mean much...we already know a larger Utility machine will be able to do a lot more work, regardless of power to weight ratios.