That cartoon is lampooning the MBS pooling that let agencies rate bundles of loans as AAA even though all the underlying securities were more risky. Bundling actually does reduce risk, but in the case of the mortgage meltdown of 2008 it was missing the forest (systemic market-wide mispricing of loans) for the trees (slightly reduced risk).
In this case, the founders already are invested in the dead cow, and so it can make sense to diversify to reduce risk. It's doesn't increase the value of their shares, it just makes the overall portfolio less risky.
The analogue to the MBS fiasco would be if the U.S. hit another depression, the whole YC class would be likely to flop, so the diversification wouldn't help, but in "normal" market conditions, the whole group would benefit from the few winners and get a payout in more scenarios.
In this case, the founders already are invested in the dead cow, and so it can make sense to diversify to reduce risk. It's doesn't increase the value of their shares, it just makes the overall portfolio less risky.
The analogue to the MBS fiasco would be if the U.S. hit another depression, the whole YC class would be likely to flop, so the diversification wouldn't help, but in "normal" market conditions, the whole group would benefit from the few winners and get a payout in more scenarios.