I do agree that the materials, if correctly specified, were quite good in the vintage period. The short stroke cranks rarely break and so are not such an issue. The long stroke ones break, BUT, they are made of exactly the same steel with exactly the same hardening processes.
The conclusion then, is that the failures were due to design failure not material failure. The designer responsible allowed the basic design to be enlarged to a point where the available steel would not cope.
It would have been quite possible to thicken up the crank, so it would have strength to match the duty with the same material, but this would have meant other mods, which meant, in turn, spending money. When Scotts did spend money, they often got their fingers burnt. Examples, Grand Prix engine, early 3 speed gearboxes, Four speed gearboxes etc. If you have spent your life in the relevant fields of engineering, you can clearly see that, not only were the designers not supermen, but they lacked the guidance of a truly gifted design director. Our response to the long stroke crank problem was to try and find a solution within the design first, but having made what advances we could in this area, it was abundantly clear that this did not give us the margin of safety we thought necessary. We therefore had to go for the most suitable modern material available to add this extra strength. For info on this material and its heat treatment see this page—
In short, I ascribe failures to design errors not materials.
All roads lead to human errors!
It’s an interesting life!