It doesn’t need to increase in purchasing power AGAINST anything. The adoption is what unfolds it as a medium not the fiat gains. A lot of people came for the NgU but once the properties of bitcoin are understood it’s irrelevant. I can provide you a service and request a payment in sats that has no bearing to its “conversion” into fiat. Everyone’s numbers are different just like everyone charges different amounts for similar services. Just because you can’t pay for existing bills in bitcoin doesn’t mean those services couldn’t be provided by someone who allows bitcoin as medium of exchange. It’s just in the very early stages.