Todd, well done. Very detailed article. Thank you for citing the paper you used. I was able to look through it to better understand their methodology.
It is fairly easy to track the performance of a benchmark like the S&P 500 over time. It is much more difficult to track the performance of something like investment real estate. No one buys a real estate benchmark as one doesn't exist.
The returns they give for real estate do not seem to include leverage, which as you pointed out in your article, boost returns significantly. Nor does it include commercial real estate, which has a different risk/return profile.
Also, for stock returns, they focus on the entire market rather than different strategies such as value investing that could help you beat the market. Same for real estate, as they look at everything on average.
With some education and practice, investors can do significantly better than average. The rate of return on my WORST rental property is 12% (compared to the < 8% in the article). The better ones are around 20%. You can buy real estate at significant discounts to the appraisal price or value, which can also be done for individual stocks, but not for an index except during a crash.
To me the best approach for beginners is index investing, as it is relatively safe and will produce solid returns over long periods of time. Then it's time to get educated about something they are interested in (real estate, business, stocks, etc) and find a way to do better than average.