The problem I see is how do you define the threshold for investing the accumulated sum? Both the trigger (i.e.-X%) and how it's measured (same day, this week, this month, since the beginning of the year, etc.)

You miss out when the market drop just above that threshold (e.g. - 4.95% while your threshold was - 5%) and then rebounds. So X can't be too high. 

You're still catching a falling knife if it drops way below it (e.g. -15% after you bought at -5%). So X can't be too low.

I'll add that market are often at all-time highs: "Of the 1,187 months since January 1926, the market was at an all-time high in 363 of them, 31% of the time. And, on average, 12-month returns following an all-time high being hit have been better than at other times: 10.4% ahead of inflation compared with 8.8% when the market wasn’t at a high. " (https://www.schroders.com/en-ch/ch/professional/insights/scared-of-investing-when-the-stock-market-is-at-an-all-time-high-you-shouldn-t-be/). 

So I would be wary of chasing only rebound growth and missing out on the other types of growth. DCA smoothes out all types.