I think to disprove zero sum, we need but one example, correct? Wouldn't one example be a company that pays a dividend? That money did not come from investors directly.

$100 to buy one share of F. That $100 goes to seller X.
Buyer Y then gets $2 dividend. Then sells one share for $100
to buyer Z. Total investor outlay is $100, but buyer Y now has $2 more than before.