It is not completely irrelevant: it is how you distinguish productive investment schemes from scammy Ponzi schemes.
Ponzi schemes are where you pay investors using the contributions of new entrants, so investors only make money so long as new entrants are joining. It's not exactly a new tradition for people to be referring to financial markets and bubbles as Ponzi schemes, although whether or not this appellation is appropriate is somewhat contested.
Bitcoin is supposed to be used as currency. The vast majority of Bitcoin owners don't do that.
That'd be true if economic actors were rational (and had total access to relevant information).
News at 11: they aren't (and they don't).