Are you a mechanical engineer? If so...

I put some spring perch bosses welded into the tube axle to see what the stresses look like compared to the batwing-style axle I did above. The results show the "weakness" of a batwing axle compared to one with integral spring perches directly welded into the main axle tube. This isn't saying that batwing axles suck either because people slap them on their cars everyday and they hold up just fine. I also analysed an axle with a nodular cast iron main tube and found that the stresses were generally lower with the solid cast iron than with the hollow tube axle of similar geometry. This all reinforces why Superbell tube axles, for example, use 65-45-12 cast iron tube ends on their tube axles and place the spring perches directly in the main axle tube (as opposed to batwing brackets welded on). I authorize Superbell to continue doing what they're doing .
The first two pictures here show the hollow tube axle with an 8,000 pound load pushing up on each king pin boss and a 400 pound force pushing laterally backward (pot hole) on each king pin. The other two pictures show the cast iron tube axle with the same loads applied. In both cases the spring perch boss is held rigidly in place.
The yield strength for 65-45-12 is 45,000 psi. So, even at 8,000 lb loading, the majority of the axle in the dark blue and lighter blue would not bend/break (according to my analysis only) and the areas that are baby blue color to greenish blue are where the axle would bend/break at 8,000 lb.