The low s/n issue...the individual arguments about it are over controversial points, granted, but the fact is that we cannot tell for sure, short of destructive testing
But it seems to me you have a Mauser question, not a Springfield question, and the question regards the dynamic between the the Mauser designs and why they are not considered 'brittle receiver' rifles.
I am not sure I follow your point about the low s/n 03s being an issue due to over-pressure however. Your statements about other rifles are fine, but how does that prove the cause of the low s/n 03 failures? Your argument doesn't remove the brittleness of those 03 receivers as being a possibility, it rather adds a second possibility.