Owning some satoshi in some exchange does not mean that this person accepts BTC at the same rate than (for example) USD. How many there are such persons for whom BTC carries the money functions (medium of exchange, store of value, measure of value and so on) as intensively as fiat money ?
I agree somewhat, but would you ask the same question about gold? I think more people are using Bitcoin as a medium of exchange than those using gold, and the value of all gold in the world is vastly higher than BTC's current market cap (7-8 times higher actually).
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Yes, this function (money function) - gold as the medium of exchange - is remarkable weak nowadays. It is so weak that it is indeed possible that BTC is stronger is this segment. But both are very low (may-be because BTC has so high transaction cost for everyday small payments) relative to fiat. I admit that BTC (and other cryptocurrencies) have strong competitive advantage in large payments between different countries. This is an excellent opportunity for crypto.