That ignores the case of feedback loops where the person who got money out of the market then turns around and re-invests at the increased price (iterating several times). Your double-entry accounting is technically correct, but that metric easily misses any “mania” where people’s expectations are highly asymmetric, and they make repeated speculative bets on that basis.
Nobody gets money "out of the market". They sell to someone else, and use the proceeds of the sale to buy another asset. But the original buyer could also have used the proceeds too buy another asset in the first place. No money is created or destroyed in this transaction.
In fact these transactions have little to do with the real economy at all, they are merely pricing assets. You can buy and sell something 100 times or 10,000 times and none of that will have any bearing on the real economy or even on things like inflation.
