As I said, there are many time frames where gold would have reduced volatility bu returns, too.
As for the data I'm presenting, I didn't not cherrypick the starting and ending dates. I just took the biggest timeframe I could consider, i.e. from start of floating dollar (*) up until now. It's a 42-year timeframe. It can be an aberration, though. But if you run monte-carlo simulations with the same tool, using historical returns, for 30-year periods, a 4% withdrawal rate succeeds 85% of the time with 100% equities, 88% with gold. For 25 years, it is 89% vs 92%. For 35 years, 82% vs 86%. No matter the timeframe, a portfolio seems to provide a higher rate of success with 5% gold than without.
People seem to have almost religious issues with gold. Either they consider it's the only worth asset, or they consider it's a piece of cr*p. I don't care about the small stash of gold I own, I just like how it enhances my portfolio's returns and reduces its volatility.
(*) Considering gold returns before 1972 is error prone because
1) gold was a synonymous for cash, so you better held STT, you would have had gold plus a return
2) well, it was almost impossible to own gold, anyway.