And how do you define "loss" and "gains" for market players?
PS: Your definition appears to be "you lost iff you left with less money than when you came in". OTOH, my definition is "you lost iff you made less money than if you would have if you'd invested it in an index fund".
zero-sum describes a situation in which a participant's gain or loss is exactly balanced by the losses or gains of the other participant(s)