Basically all Quant Finance theory is build on No-Arbitrage presumption and Efficient Markets Hypothesis.
The known Grossman-Stiglitz Paradox says: if one can't make money from trading, one wouldn't trade any asset in the first place.
I did some private trading and watched markets over time, to see that markets are indeed becoming more and more efficient, so that prices already contain almost all available information on current and expected aspects, and only random unknown news changes the market. People may agree or disagree to that more or less, but overall there is convergence to strong Efficient Markets Hypothesis over last years.
How do practitioners see this development, and why are still so many trading despite the theory?