There are reasons for the various ratings, but they do not follow engineering or safety specifications. I did extensive parts comparisons with the F350 before and after buying my F250. I also did price comparisons between models and trim levels to get the best value for what I wanted.
My current 5500 went through the same vetting, but it has been harder to find OEM component ratings on my Ram since there are so few of them compared the number Fords running around. Just try and find the real specifications of the Magna Steyr 275mm front axle verses something simple like a Visteon Sterling 10.5"...