Which is pretty clear evidence that those crashes weren't "catastrophic". That doesn't provide any proof that a future crash won't be substantially worse

Similar crashes in the TradFi space would be considered worse than "catastrophic". Media would struggle to find words to describe them.

...and that's the dilemma. Did the market rebound because there's a organic growth of buyers, or did printing tethers out of thin air help this?

Tether maybe used to be a huge risk for the Bitcoin price a few years back. Notice that we are only talking about the $ price here and not the tech.

The market is way more robust now, especially now that Ethereum is so huge and provides way cleaner alternatives like DAI and USDC.