You have a point, but by that reasoning it's pretty much impossible to prove the contrary. Long term investing in good companies, that are 'cheap' works. Not easy to prove though.

2 of my favorites on this topic:

Warren Buffet's "The superinvestors of Graham-and-Doddsville" - https://www8.gsb.columbia.edu/sites/valueinvesting/files/fil...

Joel Greenblatt "Little book that beats the Market" - https://www.magicformulainvesting.com/Home/AboutTheBook