"The later stages of the 2009-2017 bull market are a valuation illusion built on share buyback alchemy. Absent this accounting trick the S&P 500 index would already be in an earnings recession."
"Rather than investing to increase earnings, managers simply issue debt at low rates to reduce the shares outstanding, artificially boosting earnings-per-share by increasing balance sheet risk, thereby increasing stock prices."
"Share buybacks have accounted for +40% of the total earning-per-share growth since 2009, and an astounding +72% of the earnings growth since 2012."
Investment actually seems to be quite low right now by most metrics, relative to the supply of capital seeking investment opportunities. See, e.g.,  (2017)
Also, as I’m sure you might expect, the reason behind high stock valuations is more complex than this. Notably, stock represents a claim on future cash flows, and lower interest rates mean that the expected present value of those cash flows is higher when all else is equal. Highly recommended reading related to this: 
"[This could happen] if inflation forces central banks to raise rates into any financial stress."
Just in case anyone thought this sounded boring.
Thiel Macro (Peter Thiel's personal investment firm) apparently was also well-positioned for the event.
I don't blame them for extrapolating the likely consequences of central bank recklessness, and positioning themselves accordingly.
It follows a bunch of cliches from HF notes (e.g., pointless references to classic mythology and random hand-wavy macro issues). They assert a bunch of things, surround it with some facts but the overall logic is loose. There are some reasonable points here and there which lend some sense of reasonableness. But that is all a DISTRACTION.
The general goal being to give the impression of big-picture thinking when the punchline is usually A TWEAK OF SOME LONG WORN OUT STRATEGY.
Lets cut through this.
The tweaky strategy here in this case is the chart at the very end showing 50/50 mix of SP500 + Eureka hedge long vol HF index. The combination of outperforms the SP500 significantly in overall return (and in risk adjusted space). I.e., you should buy some of our HF (or your own long vol) and then also buy SP500.
The problem is long vol HF index has a ton of issues and is basically junk. It is not something you can practically replicate with long vol instruments and get anything similar in terms of performance. Additionally, a major part of the index is 2 Bridgewater funds which have fantastic performance over the period in question (especially the 3-4 years post crisis) and those Bridgewater funds are certainly NOT long volatility strategies. They are global macro. It is just constructed in a dumb way and is basically fiction. The firm that wrote the note didn't construct the index but they did select it for their comparison, so bad on them.
The classic problem with these long vol strategies is that you pay a ton of money month over month to get the return when vol picks up. And despite these strategies being generally diversifying, the performance drag kills you over time. People have looked at these strategies across many time periods, many geographies and they generally don't work. Likewise, many tail risk strategies that rely on buying options don't work well either (they can work OK under very particular conditions).
But I didn't read it as advocating a long vol strategy as pointing out the meta problem with short vol. Someone who has thought and written much deeper on similar issues is Elie Ayache. But Ayache is full on unreadable and kind of aims for a "Derrida of finance" role.
This note, in contrast, was very well written.