Reserve requirements are completely different from capital requirements. US banks are required to hold about $108 in assets for every $100 they hold in deposits, and their actual holdings are typically in the range of around $110 to $115 in assets per $100 of deposits. Central bank reserves are one type of asset that commercial banks can hold; a 0% reserve requirement just means that commercial banks can hold all of that ~$108 in other assets if they choose to.
In contrast, Tether has historically admitted to having as little as $100.20 in assets per $100 in liabilities [0], with a significant fraction of it in crypto and other assets that effectively wouldn't even count toward banks' capital requirements. It has probably dropped below $100 in assets per $100 in liabilities - i.e., been insolvent - at some point, and even taking its latest audit [1] at face value, it has far less capital than would be needed for a bank with the same asset profile in the US or other developed countries.
In contrast, Tether has historically admitted to having as little as $100.20 in assets per $100 in liabilities [0], with a significant fraction of it in crypto and other assets that effectively wouldn't even count toward banks' capital requirements. It has probably dropped below $100 in assets per $100 in liabilities - i.e., been insolvent - at some point, and even taking its latest audit [1] at face value, it has far less capital than would be needed for a bank with the same asset profile in the US or other developed countries.
[0] https://assets.ctfassets.net/vyse88cgwfbl/1np5dpcwuHrWJ4AgUg...
[1] https://assets.ctfassets.net/vyse88cgwfbl/6h4YWqZOXbwtBaPtYg...