Capital requirements are for something else. We're talking about retail customers being able to withdraw their cash, in which case the reserve requirement is the correct number.
All retail banks in the United States are backstopped by the FDIC and the FDIC is backstopped by the federal reserve. Saying otherwise is tinfoil hat thinking. Fractional reserve banking isn’t a conspiracy.
Retail banks act on behalf of the federal reserve to actively manage the money supply, in part through fractional reserve lending.
The issue for stable coins and stable coin operators, is that they’re not backstopped by an FDIC, aren’t subject to any capital requirements and aren’t subject to any risk management practices.
Capital = excess of assets over liabilities => capacity to satisfy creditors medium term (solvency)
That's at least 7% to 13% of the balance sheet for banks, and currently 0.26% for Tether.
Reserves = cash (and equivalents) in the vault => capacity to pay out immediately (liquidity)
Minimum reserves required used to be 3% to 10% of deposits, if I read this correctly, but are now 0% indeed, as you point out. Actual bank reserves, however, are much larger than what is required, even when the requirement was > 0 [see 1]. Tether holds about 5% in cash or Treasury bills.
So it seems that banks fare much better on both ratios than Tether.
It's not, because the Fed will--by law--freely convert reserve assets into cash at pre-determined ratios. Reserve requirements are an anachronism.