Every dollar that one client withdraws from an exchange was deposited by some other client. If one client has profit (withdraws more USD than he deposited), some other client will eventually have a loss (withdraw less than he deposited). So the sum of all profits and losses is zero; actually a bit negative because of fees.
Are you counting profit in BTC, or discounting BTC holdings as investments? That makes things more complicated, but in the end trading does not create dollars nor BTCs, so if one wins, someone else must lose, no?
That still doesn't say how many traders make a profit or loss; it could be that only a few smart traders make huge profits and everybody else loses, or vice-versa.