I totally agree to all what you said here, while the DCA accumulating strategy remains the best accumulating strategy, that doesn't make the lumps sum strategy bad, the most important thing is investing when the funds is available, and sticking to your investment without you tempering with it in the future.
You can lump sum while you DCA, what someone sees as lumpsum is another person's DCA, lumpsum is just in the sense of buying at once with all funds available at the moment for investment instead of spreading it . When it comes to DCA, an investor can still decide to lumpsum as Buying Dip, there're some dips that could be missed forever , if an investor spot a particular DIP and he's convinced about it them he can lumpsum as there's no point DCAing above the dip when you could have just buy the Dip. This is a choice left to be determined by the investor though, buying dips can still be done as DCA just that the amount can be increased unlike the normal amount used for interval purchases, if the Buyer is so convinced then he can just buy at once. Last year 48k was a good example, some investors might believed it will never comeback to 48k , causing them to take the lumpsum into consideration at that point by buying the dip maybe ( and that was indeed true ).