Earlier quoted context omitted.
This is circular reasoning, because if the currencies were backed by gold, its price would skyrocket to fit the GDP. You can't compare price of gold as a speculative investment to price of gold backing an entire financial system.
What if gold creates needless friction that prevents a higher GDP? For example, in a global gold reserve system it is possible for individual countries to run out of gold, possibly reducing their GDP to nothing. This happened way more often than you think and for many wildly different reasons. For example, the famous Weimar Republic hyperinflation was caused by an outflow of gold due to forced reparation payments tha…
It all boils down to a monopoly of very few organisations over the entire money creation system, and the instabilities are a result of the fact that few managers at the top are given extremely crude tools to manage extremely delicate system. Every little error using those extremely crude tools has extreme consequences.
There was always one redeeming quality of gold-backed currencies, and it's the restriction of those crude tools.
As for Weimar republic, the gold was never the issue. They were given an impossible debt to pay as reparations, and they could have that debt denominated in whatever tangible way you can think of, it wouldn't be paid. The reason the common German was devastated by the inflation was that their local currency wasn't backed by gold, it was allowed to be printed indefinitely by a government trying to fulfill an impossible debt.