My point was that entire countries economies and political systems sometimes fail. That hasn't happened in the US in the same way as it's happened elsewhere. But if it had, then "timing" the market, by which I mean selling it, would not have been suboptimal.

Maybe I define market timing differently. Holding a healthy cash position for future investment and selling investments from time to time based on either their valuation or prospects, whatever that is called, is not a bad idea.

I contrast that with being 100% invested in index funds at all times, forever. That might backtest well, but that doesn't mean it will forward test at all well.