> Cumulative return for the S&P 500 over the past 9 years (conveniently leaving out the 2008 crash), with dividend reinvestment, is equivalent to a YoY gain of 16.25%

That's a bit disingenuous to use the generational market lows of 2009 as your starting point. It would be like using the all-time highs of 2000 and the 2009 lows as your range. Then the cumulative returns would be negative ( including dividends ).

> However I think it would be foolish to presume that the stock market will continue to post those kind of gains forever.

It's impossible for any economy/market/whatever to maintain a 16% return every year.