Well, if you accept the premise that this is "fine and good", then why should[edit:n't, as in why shouldn't] the PE class beat the S&P.
Let me tell you a story that may or may not be true. We would need a study to tell us.
There are some very smart people who have noticed that debt is much cheaper than equity. They go into a company and borrow against the cash flows of the company. They borrow enough to buy the company and have cash leftover. Essentially they find money for free. In order to do this, they have to know the bankers who trust them, know how to value the firm and so forth. They go out and make a killing year after year.
You and I look at this and think, how hard can it be? We put up a shingle, and we try to do the same thing. Now we don't have the same relationships so we put everything on our credit card. We can't value the company properly and make a few mistakes. We lose a lot of money for a few years and shut down.
Let's say that when you average your and my performance with the other company, we get the S&P 500 average. And we conclude there is nothing in private equity and that there is no skill involved.
Is that the right way to look at it? Or should say that there is PE as "properly" practiced?
I suggest a simple test: if that other firm makes money year after year then there is skill. If their company is up one year and down the other, and you and I have a good year and then a bad year, it may be luck.