Well, he do admit having very limited data sets for those parts. Do you know of a good rebuttal of those chapters?
Well for starters there is selection bias. This has two parts:
1) An endowment that is well run today will probably be well run 10 years from today. As a result the well run endowments will be the largest. So if you look at the largest endowments you are biasing yourself just like if you evaluated the investment strategies of the rich by looking at Bill Gates and Warren Buffet.
2) There are a lot of different ways that you can evaluate the relative investment strengths of the rich vs. the middle class. Most of these will give inconclusive results. By settling on such an esoteric metric you are putting yourself at risk of cherry picking the data. If you ignore the 20 metrics that show a null result and only look at the 1 that shows a result you better have a DAMN good reason to pick that one. There should be a compelling case why it is more representative. But endowments are a very indirect metric.
Moving past that:
3) The praise for exotic investment strategies could very well be entirely unfounded. They could be better investments or they could be risky investments that got lucky. These are investments in extremely uncertain areas. A lot of "smart" money was proven to actually be risky money very recently.
4) Endowments have an advantage compared to private investors because they dont need to worry about life cycles. Harvard can afford to take a 200 year timeframe. Donald Trump can not.
But the much bigger issue is that his "r>g" theory throws away the conventional wisdom without so much as acknowledging it. This pervades the entire book. For hundreds of years it was widely understood that if the returns on investment were too low, less money would be attracted to investment. We have had mountains of proof of this over the past century because central bank policies have been able to create changes in real investment. Picketty says that a century of evidence is a mirage and that in fact r is some exogenous factor. Bullshit.
As long as I'm at it though, my favorite bit of Picketty stupid:
He says that inflation hurts the poor worse then the rich because the poor have assets in cash while the rich have assets protected against inflation. He also says the assets of the poor are very small, less then $1000 I believe.
Let's consider a huge jump in inflation. Push inflation from 2% to 10%. That's the difference between great moderation and oh-shit-oil-shock-iran-nuked-iraq. What is the effect for a poor person on this world shaking bout of inflation? $80. It aint nothing. But it's not the biggest thing ever. If a poor person is able to secure two additional days of part time employment over the course of the year that is a bigger deal to them then 10% inflation. Yes in percentage terms it is big but the poor are so much more dependent on income then revenues that it's barely noticeable.