Do not believe there is much wear to the axle.
The wear occurs on the king pin and king pin bushing causing bending of the radius rod.
The bushing and king pin should be on the maintenance list, since the load is applied as a single line load, which creates high contact stress on non hardened steel material and accelerates wear.
Do not believe the axle is weak for the loads it was originally designed to handle and has ample safety margin.
In my opinion the axle is under designed for front loader add on accessory.