Beating the market has been done. No doubt by many over a short period and fewer as the period increases. Also, the individuals that beat the market over a period have grasped a certain set of variables that works for that period of time and as time goes on the variables change and they may or may not recognize the changes. (And some probably just got lucky) This is what makes it difficult to beat the market over time; its dynamic. Looking at the past isn’t a clear indication of the future. The game is in a constant state of flux.
But having individual cases of beating the market doesn’t prove or disprove the hypothesis as they are almost certainly statistically insignificant, especially when the time periods are short. And remember this isn’t a natural law like gravity, its a hypothesis; A tentative explanation that accounts for a set of facts and can be tested by further investigation; a theory. This “hypothesis” is very difficult to test and has some limiting assumptions. So think of it as a way to view the world and determine if which view makes sense to you.
Obviously, financial analysts are going to believe in what they are doing and tend toward the weak form. Also, technical analysts are going to tend to not believe in any form. Both types of analysts work in major investment firms and get paid for doing something others don’t believe in.
Also, to some, beating the market seems to imply vast riches when in reality if the market is down 15% beating it would only require you to lose less than 15%. So just beating the market isn’t good enough to get you a yacht on its own merits.