Ohh and mix in the fact that it takes a literal act of congress in order to declare something to be used to legally pay debts.
I can't help but feel that you are conflating 'reserve currency' with 'legal tender'. Note that there is no requirement that these be one and the same. Indeed, most definitions of reserve currency make it clear that a currency becomes a reserve currency due to its utility in international trade, not due to legislative proclamation.
Further, anything agreed to by both parties of a transaction can be used to settle debts. In the U.S., the courts resort to the concept of legal tender only in order to have a common token in case of dispute.