They don't allow redemption of tether for dollars. There is no withdrawal pressure, right?
When you sell USDT for USD on exchange, someone is providing that dollar. If no private market participant willing, then peg slips. You would expect fiat withdrawals in downturns and peg slippage absent support.
An open question. Several attorneys general have ongoing investigations regarding the tether peg.
A really grim and cynical person might make the case that exchanges want something like tether to exist, and are incentivized to fudge the public-facing numbers regarding tether trade volume and its order book.
The set of people who have inside information on how tether functions and the set of people who would actually tell the truth about it are entirely disjoint.
Last time I checked, there were significant "limitations" (to be charitable... that you could only redeem holdings above $100K, only if you were a non-US person, and subject to 90-180 day holding periods.
People have also offered bounties for proof of people having redeemed Tether, and those bounties are still outstanding.
My suspicion is that if anyone has actually redeemed Tether, they are either institutional (and Bitfinex doesn't want to piss them off) or an insider/"friend".
Yes, USDC and USDT are different "securities".
But that's like saying that in the regular market that because Charles Schwab and Fidelity are competitors, they don't have a whole lot of cooperation - they do, because at that scale (and with the amount of arbitrage and speculation in crypto), you need to cooperate with your competitors, or you will be iced out.