You can make the same argument about any asset class. The path from Bitcoin/gold/real estate/crops to other goods or assets goes through dollars out of convenience (because your destination is purchasable in dollars). Don't confuse convenience with necessity.

Actually it is out of necessity on some level. My landlord needs me to pay rent with dollars, because my landlord needs to repay a loan to the bank and the bank will only accept dollars. The bank only accepts dollars because if my landlord defaults on said loans the bank will go to court to resolve the matter, and the courts only deal in dollars. Similarly, we all must pay taxes of one form or another, and we must do so using something the government will accept, which is dollars and not Bitcoin.

(You can adjust the currency for whatever country you might be considering if dollars are not the local currency.)

Don't kid yourself -- without exchanges of some sort (including payment processors) cryptocurrency is basically worthless.

The number of things I can exchange dollars for vastly outnumbers the number of things I can exchange Bitcoin for, by orders of magnitude.

In this case convenience is necessity, for practical, real-world definitions. Sure, in a theoretical sense, there is no reason why I couldn't use Bitcoin to buy food and clothing, make rent/mortgage payments, buy plane/train/bus tickets, buy furniture, tools, electronics, etc. But the reality is that I can't do it (with some narrow exceptions), and I don't see that materially changing within my lifetime, not to the point where using Bitcoin (or any other up-and-coming cryptocurrency) is more convenient that using fiat currency.

Yes but that would obviously no longer be true if dollars no longer "worked" (let's say 10k% inflation for the sake of argument). There would be _something_ of value that things could be exchanged for.