Or maybe you are just talking about main street investors who make their own investment decisions. I certainly don't. My advisor has total control of my portfolio and he has been extremely good. On a different level to anything I could do myself. Which is logical, given the hours of research he puts in. I prefer to play tennis.
As a Finance student myself, I've learnt to be sceptical towards "professional" portfolio managers.
Studies show that, while professional portfolio managers do make a better ROI than the index, the portfolio management fees push the ROI actually lower than the market. Additionally, there is no statistically significant correlation between the performance years of portfolio managers (i.e. that good years would be followed by good years, suggesting a "talented" investor) save for a few anomalies.
Most, if not all the time, people would be better of by investing to the S&P 500: with no administrative costs, it outperforms portfolio managers.