IMO a more interesting comparison is between trading volumes not circulating supply. the volume that bitcoin has versus different fiat currencies compared with the trading volume it has against stable coins (tether for simplicity) and the trading volume tether has against altcoins.
these values are taken from coinmarketcap.com and doesn't take into account the fake volume they report.
this chart tells us two things.
1. there is a lot of fake volume being reported by altcoin exchanges specially those involving tether.
2. the majority of tether volume comes from altcoin which indicates its main usage and purpose.