Diversification says that holding a basket of these assets rather than placing the whole enchilada in stocks would have paid off big time. A quick, back of the envelope calculation shows that a portfolio that was allocated 50/30/20 stocks/bonds/alternatives would have netted over 4% per year which is well and away the -1% stock return.
This could change things in wealth management/investment planning by convincing people that chasing the equity premium is more risky (hence dangerous) than they were previously convinced it was.