The F450 and F350 share the same M300 rear end according to 2019 fleet ford specs.
The F450 has a 1.75 spline dia X 41 spline vs
the F350 at 1.58 dia X 37 splines.
However axle dia on a full floater doesn't carry weight....just twisting the gears.
The F450 does have bigger brakes and share's the same 9900 rawr as the F350 DRW but less actual in the bed payload due to its heavier unladin rear axle weight than the F350 DRW.
In the bed payload is one reason we see more one ton DRW trucks with a DOT # on the road carrying max axle loads pulling a big heavy GN trailers. The F450 eats up money making payloads for that type work.
However with 6k + rear axle payloads they are popular with rv folks for pulling bigger rv trailers and heavy 4k-6k lb truck campers.
