BTC is just measured in terms of Fiat for easiness of trade. You can’t just say someone I’m giving you 1000 satoshi and you give me a chocolate bar because no one would understand what’s it’s worth or whether the chocolate bar is 1000 satoshi worth (example).
So you simply measure it in USD or whatever currency your country carries. It’s factual stuff and they should coexist all the time.
Replacing entire Fiat system with crypto currencies is different topic and we already know opinion about it since long. It’s just impossible due to various crypto limitations. (Supply, regulations, the way it works etc. )
Gold total marketcap is like 10 trillion at best right? Even at 20 trillion, we are going to see crypto to be much bigger, maybe even bitcoin alone be much bigger, just not right now but in 10-20 years bitcoin could have a bigger marketcap than gold.