Yes, the price in USDT terms will rise as everyone holding USDT sells it and buys something else to transfer to another exchange. But that's only in USDT terms,

Yes, the price in USDT terms will rise as everyone holding USDT sells it and buys something else to transfer to another exchange. But that's only in USDT terms, not in USD terms. So let's say the BFX price doubles as people come to this realization. You pay $20k BTCUSDT and send to an exchange where it's still trading $10k (or rather, you just start marking it in BTCUSD terms). That's an instant 50% loss. And that's assuming that BTCUSD doesn't sell off as people get spooked.