Technically speaking, the part of the shaft that is failing is not subject to any more torque than it was in the AS330, AS332, AS332L1 or AS332L2 as all it does is drive the MGB oil pumps. I am not sure torque is the root cause but this is a very ill-informed opinion as I am a Pilot and not a design engineer.
DOUBLE BOGEY-
While I understand the point you are trying to make about the modest amount of pump driving torque transmitted thru the lower portion of that shaft, in reality the torque transmitted thru the bevel gear mesh is what creates forces and moments on the shaft, housing and bearings.
I'd bet than when this issue if finally resolved, the one-piece welded shaft will be replaced by a two-piece shaft design with no welding. As always, just my humble opinion.