Earlier quoted context omitted.
> depositing USDT into Bitfinex has always immediately credited your USD balance This doesn't mean anything if that U.S. dollar balance cannot be redeemed for actual U.S. dollars. Saying "I have 1 USDT" or "I have 1 U.S. dollar on deposit at Bitfinex" is roughly equivalent--both depend on Bitfinex honoring its end of the deal.
Of course the same is true for any bank or bank-like entity, all the way up the chain to the Federal Reserve. I don't know a lot about Bitfinex, but it seems that the relevant questions are: 1) If you have "X U.S. dollars on deposit at Bitfinex", how easy is it to transfer that balance to an external account? (Maybe possible with a fee?) 2) Can you withdraw the balance in person directly for USD cash? (lol) 3) Does t…
No, it isn't. For one, ATMs. For another, bank deposits are insured. The banks, themselves, are heavily audited. In fact, "no depositor has ever lost a penny of insured deposits since the FDIC was created in 1933" [1]. (Best treasury practice is to (a) open multiple accounts, to keep deposits insured or (b) hold excess cash as Treasuries.)