To put it another way, the right tension includes a safety factor. And engineering practice specifies testing and inspection and proven materials.
Basically, it is a "solved problem" by designing things stronger than they have to be, and spending more on testing and inspection than necessary.
I'm sure the cases where these things are economical are fairly few, at least today, but if everyone took your attitude no progress would happen at all.
The Smartbolt doesn't eliminate engineering.
More importantly, safety factors; testing; and inspection are progress. We have robust assemblies built first time based on rational analysis and formal processes. We have sky scrapers, suspension bridges, and space telescopes.
Those things are progress in a sense, sure, but...
It's as if someone finds a way to make an alloy less prone to metal fatigue, and you just say "but you can use thicker metal, and test more." Sure, but.... well I don't see the point explaining this further to you, but I assume people reading this that don't see everything in black and white already understand.
I have.
You might as well argue that someone who works in a bank must understand macro-economics, or that someone in the military must have an excellent grasp of foreign policy.
You are steeped in the status quo. Your thinking on this is expected.