Right, that's precisely the currently fashionable belief system as I understand it. But I'm not entirely comfortable praising the US economic system in the fiat-money era 01971–02024 by comparison to the previous 53 years, 01918–01971, which were the last 53 years of the commodity-money era there, except for a short break in the 01920s. I think everyone agrees that the US economy developed in a qualitatively better way from 01918 to 01971 than from 01971 to today, and that there was a sort of discontinuity around 01971.
It's possible that the mainstream economists are right, and that things would be far worse without the shift to fiat money, and it's just a coincidence that it happened at the same time everything started falling apart. We don't have anything like a controlled experiment. A lot of things happened to the US around 01971: the Vietnam War, the Civil Rights Movement, the end of the Apollo program, the War on Drugs, the New Age movement, CREEP, rapprochement with the PRC, the energy crisis, the Clean Air Act, second-wave feminism, Love Canal, etc. Most of these seem like things you'd naïvely expect to reduce domestic economic inequality, though, however detrimental they might have been to the residents of Taipei and especially My Lai. So why did it skyrocket instead?
PG has an innocent explanation: as I understand it, he thinks companies suddenly had to compete for superstars in the job market, abandoning seniority-based pay and thus creating the yuppie and growing wealth inequality. But a plausible alternative explanation is that fiat money rewards elites in nonobvious ways, enabling them to concentrate ownership of the economic base in a smaller and smaller subset of the population. Certainly that was the merit Marco Polo claimed for paper money when he became the first European to describe it in writing.
It's not a widely accepted theory today, more associated with crackpots actually, but it certainly isn't new.