There is alot of things that matters when allocating obv.. Politically, Monetary police, P/E P/S in the stockmarket, Debt, upcoming wars, what is happening in the world, bonds, rate hikes, real estate, etc...
Think of it like this: There is tons of ways the stockmarket could end in chaos, tons of unpredictable ways, tons of variables outside the stockmarket that will have an effect on the stockmarket... These "ways" have been brewing since 1970's and the bubbles has yet not popped, getting bigger each year.
Gold has value on its own, protects against everything above + only one VERY UNREALISTIC way the gold market can end in chaos
No matter how you look at it apart from this data u should allocate some of your money to either spot gold/physical in your portfolio before the data suggest otherwise