Financial trading of any kind is zero-sum (actually negative if friction is added). Stock investing may not be zero-sum but can be turned to one with suitable choice of performance index.

Markets are not efficient, however knowing the model to take advantage of the inefficiency may be difficult. https://medium.com/@mikeharrisNY/efficient-market-hypothesis-the-biggest-farce-in-history-of-finance-and-economics-3f69c8e0de45