This response is for outside observers rather than to continue to argue as I have no expectation of convincing you of anything.
I don't believe the coolant systems broke until after the hydrogen explosions. The Atlantic article cites anonymous sources making these claims, which I just don't find credible since they fly in the face of many other sources of information. I am assuming you think there is some conspiracy by the nuclear industry to hide the broken pipes. The other article you posted is about a pump that failed 5 years after the tsunami. Also, convenient that now the switch gear was destroyed by the earthquake too.
Why don't I believe what you propose:
1) Units 5 and 6 survived because the generator and switch gear were protected from flooding. The building and coolant system designs were the same and they did not meltdown.
2) The double ended shear failure is considered not credible in the industry. You may not be proposing this exact failure mechanism, but as a result of this paradigm in the industry in service inspections (ISI) plays a big role. In service inspection plans are implemented on safety class pipe to monitor thickness and cracking, which regularly use UT to verify the condition of pipes. These activities are covered by the American Society of Mechanical Engineers (ASME) boiler and pressure vessel code (BPVC) Section XI.
3) If this accident were simply due to pipe failures, it would be better for the nuclear industry. That is an easier problem to deal with than the issues that have been brought to light due to this accident and the ones before it (people and management failures).
4) These systems are very robust. I base this off my experience with them. That is not a great reason to convince anyone else but it factors into my opinion.
You reveal that you don't understand the technical details you are trying to argue by invoking "military grade". Nice that you included helicopters in the story to make it sound impressive. The term you should have used if you wanted to sound like you know what you are talking about is Safety Class. That is a nuclear term and means something in the industry, but not really relevant for generators in this case. "Military grade" doesn't mean magical.
There are reasons to question the merits of nuclear power, just not the ones you are making.