What I think you are implying is that if you invest in companies part of some market index¹ and end up above the average performance of this index then someone else, who also invested only in companies in this index, will end up below the average.

This however is not zero sum game or has anything to do with markets or investments, it is just how averages work. You could apply the same logic to grades in a school class.

¹ There are lots of market indexes and they only cover a fraction of the investment possibilities and are often trade specific.

I think what you are saying is that if everyone invested very intelligently, then everyone would be better off, as more money would pour into the more viable ventures (is this what you mean?) I can agree with that, FWIW, but from the short-term algorithmic/high-frequency trader 's perspective (edit), this does not appear relevant (some nth order effect).

P.S. Traders often say how their work is useful to everyone, because it makes the markets more efficient. I wonder if it's true. The analogy I'm thinking about is frequent lane swervers on the freeway ("lane arbitrage"). Are they making the freeway more efficient for everyone? I don't think so.

All I was saying is that it is not a zero sum game.

As for invested very intelligently I don’t think you can define that, nor what it means for everyone [to] be better off and more trading of a stock does not mean more money go into the company the stock represent (assuming the stock is not sold directly by the company).

This is all very long-winded to get into here, but as a quick example of how this “intelligently” and “better off” is ambiguous I think we would be better off with more alternative energy, so people should invest in that. But a lot of these investments will likely turn out to be non-profitable (even cause a loss) but on the bright side, a lot of R&D in alternative energy will be done, which is good, and those companies with good projects may end out making a difference in the world, etc.