My (much less than 50 years of) experience bears that up.
I started my 401k in mid-1998, and it is not doing well, return-wise. I don't have the numbers, but I'm pretty sure it's less than 5% per year*. I started directly buying stock in early 2009, and am up over 25% (not counting dividends) on my portfolio in less than two years.
Of course, I would think that the last decade has been unusual, but a less extreme difference over 50 years might have the suggested result.
* (based on total amount contributed over all years compared to total value now, which probably isn't the proper method of calculation)
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