The large Dutch pension fund ABP achieved an annual return of about 6% over the last 20 years, according to https://www.abp.nl/over-abp/duurzaam-en-verantwoord-beleggen/beleggingsresultaten. The S&P 500 had a 10.392% return (dividends invested) over 20 years, according to https://tradethatswing.com/average-historical-stock-market-returns-for-sp-500-5-year-up-to-150-year-averages/.

This means that if you would have put €10.000 into the ABP in 2005, then that would have compounded to 10 000 \cdot 1.06^{20} = €32.071 today. If you would have put that money in the S&P 500 instead, it would have compounded to 10 000 \cdot 1.10^{20} = €67.274.

This means that you would have roughly made twice as much money in the S&P.

One caveat is that there is a 25% dividend tax here in the Netherlands, which would made the difference a bit smaller, but not much. Dividends are typically about 3% as far as I know. A tax on this would mean 0.25 \cdot 3 = 0.75. So say, 10 000 \cdot 1.09^{20} = €56.044 which is still almost twice as high as the result by ABP.