How does bitcoin solve this? Last time I checked there's no fixed bitcoin price either. The currency is so volatile on news, it's sagging and spiking all over the place.
Likewise, a Bitcoin is worth what a Bitcoin is worth.
The difference between the two, what the OP is pointing out above you, is that Bitcoin currency has a limited supply and so can't be devalued. Relative to each other, a Bitcoin will increase its value to the USD because the supply of the latter is always increasing.
Bitcoin is a massive waste of the natural resources used to create and maintain the blockchain entries, nothing more, and probably won't ever be anything else. A properly designed cryptocurrency could be useful, but it won't look anything like bitcoin.
Until Bitcoin crashes entirely, of course.
OK, new topic: Draw a graph of each currency's Big Mac Index, or how much of each you need to buy a Big Mac in some major American city over the same timeframe. (We could do the same thing with Wonder Bread or a dozen jumbo eggs, but the Big Mac Index is actually A Thing.)