This is one of the things I do for a living, and the study is right, but there are two issues that should be addressed first. First and foremost, most Americans in the 99% simply don't have any financial education. Our schools don't teach kids what a mutual fund is - so why would they grow up and use them in a smart way?
Another issue is risk. High-returning investments always involve risk, and estimating how much risk a client can bear is an art, not a science. Time horizon, financial position and psychology are all important.
Unfortunately, the folks who are really expert on this stuff generally don't want to spend their time on anybody with less than a million to invest. For most of us, it's hard to get good advice - and 100 other things also want our attention.