And yeah if there are only. 56 million truly funded addresses we both know people that have their own addresses have two or three or more.
One shouldn't forget that most members of this forum are in the upper 10% of Bitcoin users when it comes to knowledge about how Bitcoin works. The more knowledge, the more addresses people tend to use, for privacy reasons, the quantum computer topic etc.
Many "small investors" with limited knowledge have a hardware wallet and I would guess they tend to store everything on the same address. So my guess is that the lower 50% of "real" (on-chain) Bitcoin owners could have indeed only one address where they store everything. Many came to BTC from Ethereum and other altcoins where it's even more common to use a single address.
The other 200-300 million (I don't know how exact the crypto.com numbers are, but I would not be surprised that 80-90% of "Bitcoin owners" are only "IOU owners") who "own" only IOUs however also do incide in the market. Either as potential demand or supply, they thicken the order books and thus create liquidity. That's actually what this thread is about I think, although you're of course probably right about the OP's intentions.
Yes, fractional reserve is a possibility but I don't believe it to be widespread. It's probably too dangerous for the big players.
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).