I'd like to see your source information for the welds being "orders of magnitude" lower than the parent material. Because in general welds are not modeled as that much weaker than the parent material in an engineering setting. The strength of the weld is dependent on the parent metal and the filler metal used, but orders of magnitude weaker is not common at all.
Welded correctly those UCA's would likely outlast most of the members on this board, myself included. I myself would likely replace them, but only because of their unknown provenance, not just because they were welded.