To be fair the total annualized return of the S&P 500 over long periods is roughly 10%. You don't have to reliably beat the market to reach those numbers. It's interesting to play around with:

https://dqydj.com/sp-500-return-calculator/

I think you forgot to click the “inflation adjusted” checkbox. The real rate of return is closer to ~7%. Also caveat emptor - past performance is no guarantee of future results.

But the calculator you're criticizing does not adjust for inflation...

I think that’s the point. A projected savings balance is misleading without considering inflation, so if the calculator doesn’t make an explicit adjustment for it then there ought to be an implicit adjustment in the rate of return assumption.

Says who?

Projecting historically low inflation is no less reckless than ignoring it. Imo, you're better off looking at absolute returns and tweaking your expectations based in inflation as itnhaopens.

On the other hand, the Nikkei's still underwater from its peak almost 30 years ago, and has been more or less flat since 1995.