Paul,
Whilst not disputing the facts you present, there is a logic dis-connect between the evidence you produce and the conclusions reached or at least implied in your article.
You argue, persuasively, that the STC to increase the MTOW on the Shrike was not justified on a PERFORMANCE basis.
The accidents in question were due to in-flight failures. Whilst you draw the simple conclusion that more weight= more stress, you do not present any evidence, or even opinion from the manufacturer, that the increased MTOW was in any way related to the in-flight failures.
What evidence do you have that the aircraft, even if they had spent their lives operating at the original MTOW, would not have broken up under the stresses present in these accidents?