You can do DCA (Dollar Cost Averaging) regardless of the price if you've done your homework, studied the asset you're buying, and know it's a top-quality asset. Although, as you said, downturns can be ideal times to buy more than usual.
Yes, this is what DCA means. Regardless of the price, you can continue to buy bitcoin. But people have different approaches or strategies of buying bitcoin. Bitcoin is not an asset that continue to increase. If you study the price when it was at $59800 to when it was at $109900, you will noticed that it was bull market but there are times it retraced which are good time for DCA. Simply to DCA at anytime at any price is commonly done by people that are not ready to make analyses but to just buy. I prefer to wait, make the price retrace and I buy more which I saw as a useful strategy.