What caused all the supply chain bottlenecks?

If you have a substantial buffer, when demand picks up you notice that you are drawing from your buffer at an increased rate and you order things early so that you can scale with that increased demand. It's okay if your suppliers need some time to hire additional labor or buy a new machine, even at this increased rate of consumption you still have some time before your stocks run out. There is no need for you to pay your suppliers a premium to drop their existing orders from other customers to support your demand.

If you don't have that extra buffer, then when demand increases there is no avoiding shortages - not only do you need to scale up to increase production and meet this new demand, but now you also have an ever growing backlog of orders that you also need to fulfill. These companies scramble to rush in material and equipment asap, which drives up prices and drains the stocks of other companies, and pushes the problem further up the supply chain. Firms that aren't actually seeing an increase in demand nevertheless must buy more to guarantee their buffers will not run out, further increasing shortfalls in production. What could have been a localized hiccup cascades into a global economic problem.

However it's important to note that the pandemic was not simply a shifting in demand patterns. Early on production in many cases stopped or was extremely reduced as employees quarantined and businesses cancelled orders expecting various drops in consumer demand. Again here, JIT is a problem as it led firms to cancel orders much earlier than they should have, and it makes restarting lines much slower. For example auto makers cancelled their chip orders right away at the start of the pandemic expecting people to save money and not buy cars, but it turned out demand for cars increased, and a lack of chips grinds auto manufacturing to a halt. If the auto manufacturers had just accepted that their inventory of chips might sit on a shelf a little longer, the counter intuitive uptick in demand would have been a blessing instead of a curse.

Now you've gone in a circle. That's what the original comment was talking about. This subthread is hinged on the idea of that specific problem not happening.

(You didn't ask me and I'm not an expert but) Not if you just use them as a pure buffer (and there's no re-re-adjustment before they're used up), no. But they'd give you some time to think 'Hm, stocks being depleted faster than usual, we need to reorder sooner, and more.'

Obviously, but again, the point isn't who's at the very top of the leaderboard. The point is that the material situations of the top, say, 500 richest easily allow for what we plebes would parse as insane economic loss in real wealth, and they'd be basically OK with it. Perhaps they'd no longer be in the top two digits, but they have only really lost in the sense of a high score, not lost in the sense of total dispossession and now your life's over.

If SpaceX was somehow destroyed, reputationally and materially, Musk would still have Tesla, and all his other ventures and economic instruments. Likewise Amazon could go belly-up due to a sudden locavore craze and a drone uprising, and AWS would continue making money hand over fist. My point is that the owner class is thus not actually seriously incentivized to prevent an economic crash, and in fact their apocalypse-bunkers indicate that they're pricing in the clearly non-zero chance of it happening.

Lastly, the numbers you're using about the ages of these mega-corps? Good point about that -- the Hudson's Bay Company once owned more land than any other company ever, acted as first contact to uncontacted Natives, and now they are a department store. That said, I don't think Amazon or Tesla will fall from grace in the near term. Blithely assuming that the HBC, like many a corporation, would have a 20 year lifespan or even just wane in power in 20 years, would have been a bad bet in 1700.