The problem with SP500 is survivorship bias, obviously the "top 500" companies is continually redefined every year and is, after all, the top companies, so you'd expect a much better return from a subset of the best companies rather than the market in general.
Something like Wilshire Index returns 7% CAGR over the last 20 years. Interestingly, Russell and Dow are about the same 7%.
As the economy becomes ever more permanently unequal, the concept of one number representing inflation becomes less meaningful because there is no longer one standard of living or one cultural expectation. Something like M2 is 14000 now and 4000 in 98 so thats 6.4% annually. After tax the Wilshire would only return maybe 3% or so, minus 6.4% inflation, whoops... Or you could use the famous Big Mac price index which is about 2.8% over the same time period, leading to a very slight profit of a fraction of a percent. Are you part of the separate subset of society that lives off M2 or off big macs or ...?
So investing in "the market" depending on hand waving provides a modest negative to approximately zero return. If you can pick the subset of winners in advance, the SP500 is quite profitable, although if you can pick winners in advance there's probably more profitable things to predict.
Also remember the market can remain irrational longer than you can remain solvent over all values of "irrational" or "solvent" or "longer". I have a medical insurance bill to pay next month, not over ten twenty or hundred year average. Pulling out a constant sales price from the market to live draws down a balance faster than pulling out a constant small percentage of total value over a long time period.
Then of course there's long term demographic issues. The USA is supposed to be richer in the future because... why exactly? You might get a bigger slice of the pie, but theres no particular reason to expect the pie overall to expand.