It's mentally and financially attractive to engage in DCA rather than lump sum (including practicalities of the real world rather than fantasies about having funds available that are not available), and DCA practices also may well end up allowing someone to be more aggressive in their BTC accumulation as compared with lump summing it, which is more than just mentally comfortable but ends up resulting in the concrete and material buying of more cornz that ends up paying off, if the BTC price ends up going up.
You're correct. It's easy to look into the past and come up with schemes that would have made you a lot of money, the question is whether they will continue to make you money going forward. Even PlanB poses the proposition as a question. As well with what you say, DCA may not be optimal but that doesn't mean it isn't the best, depending on what criteria you judge it on. Not that I'm saying it is the best (a hybrid approach is probably preferable for most people), just people should be wary about 'make money fast' schemes. They often contain elements that will leave you without a shirt if things go wrong.