Yes, I agree that the strict interpretation of Gresham's law is not exactly applicable here, since there is no enforced BTC-USD rate. But the broader sense can still inform, along the lines of Rolnick and Weber:

> They also focused mainly on the interaction between different metallic monies, comparing the relative "goodness" of silver to that of gold, which is not what Gresham was speaking of.

(from the wikipedia article)