> Taxation is the underlying "backing of violence" that helps makes USD so attractive

It really isn’t. If the U.S. shifted to a system of tariff-only taxes, the dollar would still be in demand. If the U.S. let income taxes be paid in the currency of the payer’s choice, most Americans would pay in dollars and irrespectively the dollar would be globally demanded.

There simply isn’t much empirical proof for the taxation hypothesis of the value of money.

Every single taxable US transaction having a non-zero component that must be settled in USD seems like a pretty strong empirical piece of evidence as to why the transaction would settle in USD. You can point to back when US funded itself mostly on tariffs, but I don't know what that would prove, because at that time USD was backed by gold (or silver).