> that US cash has absolutely awful usability compared to the Euro.

Euro bills differ clearly in color and size, which means they are quickly identified.

Also the Euro coins differ in shape and size quite a lot, which is easy to identify blind even when handled individually. More than U.S. coins which are more similar.

I don't know about an objective difference caused by the fact that 1€ and 2€ are coins and bills start only at 5€ whereas the one dollar coin isn't much used in favor of the one dollar bill.