Maybe you looked at the people with below average experience with securities, and I looked at the above average securities investors/traders.
Yeah, you do not need to go to Top 5 MBA Finance school with CFAIII and/or CMT to be an market expert.
Again, cap gain isn't the only way to play market. You can get a consistent income from market as well with less capital than real estate.
Don't get me wrong. People around me do all sort of deals besides securities.
Some people make more during Bull market, and some just do better during bear market.
As you mentioned the 2000 internet bubble, I've seen lots of people who lost majority of their $$. In contrast, I've seen people making tons of $$ by shorting and puts on high earnings multiple stocks to nearly zero.
I recently had a failed acquisition on private equity deal up north. I do value the residential/commercial real estate as well, and know the perks.
Although, I am not a "private capital/equities" or "Leverage Buyout" expert, but I do know some enough to make some $$ for a company I use to work for when I was in late 20s.
I believe your friend is definitely better off invest heavier on residential/commercial real estate than a market.
I do know a kid who is in grad school at CU, and he is making about same net on selling out-of-money puts (again lotto options) with far less capital. He does that every month to collect premium.
Your friend doubling his retirement in 2 years on a real estate from bank's leverage is impressive.
Apple with ~550% in 5yr average is impressive? I am sure people who ONLY invest in real estate would say it is LUCKY.
Forget 550% in 5 years. Would you believe me if I told you that my wife had approximately 2000% CALCULATED (no luck) return her retirement within 6 years off of her ESPP/401K alone?
To reply your last statement. Why are you comparing a real estate to a DJIA? I am sure you know better.

Indicies or Index funds ETFs are for people who just want to have a ride to the market. S&P500 with < 50% gain?
Even a no brainier stocks like NFLX or BBY with LESS THAN 2.0 risk multiple had over 150-320% gain YTD. Oh yeah. that is just on Investing LONG without making INCOME off of writing call/put.
I think people should compare $X/yr income real estate investor to $X/yr income securities investors. Not $X/yr real estate investor to Negative $Y/yr securities investors.