As for the stock market, there are scientific studies (they are possible since the entire trading history is available) that show that shorting on average is unprofitable and buying is profitable.
Can you share the links to the studies, or where did you get that information? Because I've encountered the opposite: that short selling, though very risky, is more profitable. You just have to be an experienced enough trader. Of course, for a newbie, who doesn't yet see how the stock market functions and some general tendencies, can't expect certain price values it must be difficult, but is it unprofitable for the skilled traders as well?
I cannot give an example of a specific scientific study on this matter, however, the conclusions about the constant growth of the stock market seem logical to me.
1. The modern economy is inflationary.
2. We also live in an era of technological progress.
3. The world population is constantly increasing.
4. The price of gold, silver, platinum and other precious metals is artificially constrained by the derivatives system.
5. Investors, in an effort to preserve their savings, invest US dollars in stocks.
6. Companies are constantly reducing their costs and maximizing profits.
7. The number of consumers in the world is constantly growing.
This leads to an increase in the capitalization of the stock market in the long run.