it can make some sense strategically to ride it up so long as it is clearly continuing: until there are no longer signs that the bull is still underway.

That's why watching something like the 200 day SMA of the s&P500 is a reasonable thing to do.
A clear sign that the bull market is over is that it is going down long(ish)-term. Long average to smooth over short-term irregularity.


So the extra gains you see during those stretches are always going to go away unless you sell while they're still high.

Ditto.

Way back 'round about, I think, 2010-2013 we had a very long debate/discussion related to this.
One side was all "Who can stand seeing their portfolio cut in half? It wouldn't have happened in [this here strategy]"

The other side was all "Okay, sure, [my favored strategy] got cut in half down to $500,000. I lost half a mill. Your strategy only lost 10%, from $100,000 down to $90,000. Last time I checked $500 is more than $90."

Of course, that doesn't help if you started investing shortly below the peak.