When you say "index-like performance", what index are you referring to? That's a very vague statement. Care to elaborate on what periods this fund delivered "a small margin of outperformance?

Large value or large blend, the fund is typically somewhere between those two.  The fund has a .89 R^2 with the S&P 500; you might compare that to more focused funds like FAIRX (.44), OAKLX (.67), or their very own CFIMX (.74).  The numbers will jump around over time, but in general, funds with large asset bases are going to behave more like the closest market index.  If you compare the fund to VFINX or VIVAX, the fund has outperformed by about 2% or so on an annualized basis. 

And even if the managers managed 100B in assets with all their mutual funds and private accounts, it makes little difference. 100B is small change in the world of mega cap stocks.

Sure, once you restrict the universe to mega caps, it's small change.  But the whole point is $100B restricts you to mega caps.   Making big returns off of mega caps is difficult.  Fewer mispricings, fewer opportunities for outsized returns.  Not impossible, but harder. 

Best,
Oildog