Why anyone invests in any VC fund, when you can do better in the stock market with an index fund, at much less risk, is beyond me...
Perhaps, but we don't really know how much risk many of those VC funds are actually taking. With liquid, publicly-traded stocks we can sort of use variability of returns as a proxy for risk. But there's no equivalent good way to really quantify VC fund risk. Sure you can do risk modeling but it's just an educated guess.
Distribution of returns. Longitudinal volatility is a (good) proxy for this.