"then the FAA would have mandated the replacement or overhaul periods at least Fifty years ago, which it didn't."
Because Sunny the FAA completed your points 1 to 4 as a proper regulator with "Foster and Promote" in their charter and concluded it wasn't necessary.
I understand the statistics bear that out, with more catastrophic failures from overhauled engines than those on condition.
Then by and large the FAA employs "Competent" people not dross from the bottom of the gene pool who are legends in their own minds.
My father always said when I learnt to fly, "When you think you know it all give it up and do something else". Unfortunately our ex military and failed industry masters have nothing to learn about aviation, the rest of the world knows nothing about aviation, CAsA is the font of all knowledge and their Philosophy of " Better to die safely than live non compliant"