This is actually untrue, bitcoin can be used as many things, and unless the price is zero for all eternity, which at this point appears to be extremely unlikely

This is actually untrue, bitcoin can be used as many things, and unless the price is zero for all eternity, which at this point appears to be extremely unlikely, it can be used at the very least as a wealth transfer medium. There is nothing in that particular use case that particularly benefits from a rising or falling or stable exchange rate, only a non zero one. As a store of wealth, bitcoin is probably better off sitting at a single stable price rather than climbing exponentially as it has been, so even in that case it doesn't make sense to class it as a pyramid scheme. Pretty much the only scenario where it makes sense to class it as a pyramid scheme is as a speculative investment. And frankly, if the most horrendous negative externality of bitcoin is that people are able to engage in speculation on distant value and are exposed to the risk and reward thereof, that really doesn't sound like a huge criticism to me.