Why would stock market valuation be a good metric? If Walmart's valuation doubled in that period, does it mean they sold twice as many goods? How could salaries hope to double, if the things people buy with salaries didn't also double? Did Ford's vehicle sales double in that period?

If these things aren't happening, then what would be the point of salaries doubling? If they gave me a raise tomorrow of $150k, that'd be great. I'd be sitting pretty. But if they gave all of us an extra $150k starting tomorrow, none of us would be better off materially... the inflation would eat up any gain whatsoever.

The only reason the stock market valuations don't do this is because the vast majority of us aren't buying stocks. That money's illusory. So no, it's not "really as simple as that". For all this supposed productivity that you claim, there's not been any significant increase in product.