As others have said, we only know the behavior of drops in hindsight. During the fall, at any point, it can still go back up, or down some more, or stay flat for awhile. I’d suggest studdying the 2008 event, this one was full of false rebounds (on top of the uncertainty of still having your assets the next day in case your financial institution went belly up).
In case you’re interested, I’m conducting a similar experiment: Timing the market using moving averages - an experiment
The goal is simplicity and drawdown reduction. While I’m confident the 20-4 strategy should improve returns on the long term (but requires selling assets held for less than 6 months at times, so may bear some taxable risk if implemented at a larger scale), I have no guarantee for it and that’s not a bet I’d be willing to make.
I see it more as a way to use a more agressive asset allocation (so the gains come from holding more stocks in good times) than a returns winning strategy in and of itself.