This is perhaps the most important topic of out time. Many times, the value of the business diverges sharply from that of the market...witness the 2000 period dot com runup as an example. If you were the holder of a pension asset during the period, your interests will ill- served by money managers chasing an index so as not to underperform and lose clients. of course, the pension holder suffered greatly form those who indexed their funds in the subsequent period.
Another way of saying this is to look at vanguard- a firm which indexes for a living. look at their returns from 2000 and ask whether one wouldn't have been better off in simple corporate bonds.