This assumes that the backing assets: 1-actually exist in the claimed amounts, and 2 - are easily liquidated in a timely fashion to provide cash to USDT holders

This assumes that the backing assets: 1-actually exist in the claimed amounts, and 2 - are easily liquidated in a timely fashion to provide cash to USDT holders when they trade in. You can cause a liquidity crisis in USDT if either of those are not true.