They aren't brokerages, they're banks pretending to be exchanges. They do fractional reserve banking with user deposits.
Nobody backstops FTX or any other crypto exchange so its better described here as 'the yolo lifestyle'.
A modern day bank run in traditional finance is functionally impossible* (up to the FDIC insurance limits, and often higher in practice - there were no imposed limits at WaMu for instance).
Levine spoke about brokerages. When brokerages extend credit, they can be subject to run dynamics. Not exchanges.
There's a reason the perp exchanges have a fund, it's the capital that protects them from losing money on overleveraged customers. Or rather it's the rainy day fund that they lose out of when the delev happens.
Not sure this is related though, mechanics of today are not clear to me from what I've been able to find.
Not at all. Bank runs still happen, the backstops just soften the blow with liquidity injections. Every time you see a withdrawal limit, there is no doubt a bank run is occurring.
This is not accurate. Withdrawal limits are there to control fraud.