I think covid and the silicon shortage has shown us how JIT manufacturing completely falls apart if there's a delay in just one of your components.
One thing people don't generally know is that as developed in Japan it's a quality control system. If a jig at a supplier gets out of alignment and parts made with it are out of spec and not noticed until assembly, you're better off with a feedback loop measured in hours instead of months.
COVID and the silicon shortage ... I'm not even sure JIT has any relevance, one of the biggest problems in the US was car makers canceling orders when as you could easily predict from historical plague patterns the demand for cars would go up as people left cities. Demand for a whole bunch of things changed due to the secular changes in the economy like work from home, JIT's shorter feedback loop might even help with that.
But chips are indeed one thing that shouldn't be done in JIT style. They inherently take a long time to make and are relatively easy to test. Toyoda was said to have changed their inventory strategy for them after the disruptions of the earthquake and tsunami.
And then there are disruptions like a fire taking out a fab line, I remember this happening in Japan for embedded type chips. Unlikely any relevant inventory policy would save you from that especially if there's an increase in demand where stockpiling won't save you.
The industry can't even in theory surge old nodes for which the equipment is no longer manufactured. We hear a not uncommon pattern is that they'll just suddenly stop making chips forever because they can no longer fix a critical machine.
You're correct, but that still doesn't address the quality control issue for things like metal bending, unless you add intense $$$ inspection to the process. You still have X amount of inventory of items you haven't yet assembled into cars or whatever for the final test of quality.
OK, for some of the upstream problems you could spend extra money to statistically pick individual items out of a designated stockpile/buffer and assemble them.
But stockpiles work better for stuff that can be tested, like piles of ores and elements or at the complete opposite end chips and electronics that can be tested , and nowadays we have the transistor budgets for self-testing.
It seems like the More Bad Advice crowd wants to keep living in a fantasy world.
It was not as bad as the COVID lockdowns, but at the time the changes were pretty drastic.
A lot of overhead was added for security. Now you need ID to get into a lot of places you did not need before. For example: my uncle was a UPS driver, and he said before 9/11 people just saw the uniform and waved him through. Bottom line, I think 9/11 showed there was no slack capacity, and a lot of companies struggled. I guess companies just adjusted to the new reality.
I do remember reading articles/web pages questioning JIT, and stating that if there was more slack capacity adjusting would have been easier, although I cannot think of any specific URLs/writers at the moment.
I am just a software grunt, but I feel like I have seen a similar dynamic in every job/project I have been on. Management keeps yacking about innovation, and pushing more work on us, while dismissing the notion that more time and/or more people would make everyone's lives a lot easier.