Earlier quoted context omitted.
The companies that compose the entire stock market also change all the time, and follow the same pattern (winners rise, losers go bankrupt). So the S&P 500 is still a good benchmark of overall stock market performance.
So as long as innovation is outgrowing stagnation then returns should continue to outpace typical zero risk interest. In essence if you believe the stock market will fail to exhibit growth you’re betting against technological progress and productivity gains. Bad bet I’d say.
Who are you arguing against? The paper linked talks about "significantly lower profit growth and stock returns in the future" not about decreasing earnings and negative returns.