Absolutely true, physical cash, well used, can be invisible. But personally, I don't see moving a million in bills as the same as moving it online (in terms of logistics, risk, and speed). Bitcoin leaves a mark, yes, but it also allows for the movement of large amounts of money without borders or intermediaries, and that has a power that cash simply can't match. I say this with certainty, because I did it when I left Cuba, coming back with a handful of satoshis without anyone knowing (or even seeing it).