Yes, while market cap has its flaws, it's certainly not useless. It's most commonly used to compare the size of asset classes like Gold, Stocks, Bonds, etc. Realized cap, is a better measure of money invested, but it is not available for other assets.
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The illusion of market cap is also why unrealized capital gains tax is a completely insane concept regardless of whether you are for or against taxation. I love the realized gain metric on Btc, it's like a brand new world of data.