Heh heh. Sure you have seen all axle wallas weld axles. But you did not ask the owners of there cars how long these axles last?
With reference to the bold items, let me ask you these questions, After welding, was the welded shaft put on a lathe machine and checked with a dial gauge for trueness (the amount of bend in the shaft after welding)? If so how much run out was found and does the axle walla or lathe walla know how much run out is acceptable? Or before we even go to the lath machine, was the correct electrode used based on the metallurgy of the axle shaft? Was there a bevel of an included angle of 60 degrees in both shaft parts prior to welding? And then was post weld stress relieving done?
There are a number of technical considerations in the business of axle welding. Two bits of shaft just can't be thrown together and welded. Which is why I go back to my original comment about your continuing headaches with the axles as long as you travel down this path of using welded axles. I hope I have answered your questions