Cryptocurrencies marketcaps combined are now around 330 Billion USD, which is roughly 7.5% of cash in circulation in Euro and Dollars combined (around 2500 Bn USD)
Maybe I just didn't get your point but it seems like you are trying co combine the market cap with the amount of existed fiat money.
Market cap is calculated as the price of the last coin sold on the market multiplied by the number of coins. So for example if you are buying a coin for 2$ that was 1$ before then you doubled its market cap (for example from million to 2 million dollars if it has 1 mln supply). You can hardly get the same amount of fiat money if you try to sell all crypto.
That logic is not working with fiat mainly because it is not traded / used the same way as crypto.