Agree. Take the Vanguard Wellington Fund, for example. It is basically an index of value stocks and high quality corporates & treasuries, in roughly a 2:1 ratio of stocks to bonds.
The fund started in July 1929(!), and has returned about 8.5% per year on average over nearly 70 years.
Personally, I invest monthly amounts into the Vanguard Total Stock Market Index fund and their GNMA fund, at about at a 1:1 ratio. Such index investing is simple, cheap, and has proved itself over long periods of time.