"Even though they temporarily monkey hammered metals down to appear to crash a small amount along with equities, they then had to initiate QE right afterwards in order to prevent the system from grinding to a halt, which saw the price of metals jump a lot. Had they not done QE and just let the system collapse, those assets near the top of the Exter pyramid would have been rapidly decreasing in value far more than stuff like metals at the bottom, so you gain in purchasing power regardless."

Excellent point. PMs can win even in scenarios like relevant devaluation compared to other assets.

One of the factors for this is that PMs are global while real estate, stock markets, etc are national. Say there is a large deflationary economic crisis in the US. People start selling their land, cars, stuff, stocks etc dirt chip, due to searching for liquidity. They are also selling (some of them) their metals. But at that same instant, in some other country with inflation or devaluation, this extra supply of metals is a gift from heaven because they can buy PMs on discount. But they can't really buy american land, cars, boats, stocks, etc (which leads to further crushing of their price due to barriers between economies).