you're right one using lump-summing to start his Bitcoin investment is also a nice start up. It would make one to have some nice quantities of Bitcoin,  But it depends on the price at that moment, because using all at once when the price is high won't be encouraging at all expecially when you are new in this space and with the mindset of making short-term without any proper plannings ( at that moment you are no longer investing but gambling) , such individual purchasing bitcoin with lump-summing when the price as surge (increase) . And after such individual as purchase Bitcoin during such time and then it began to dip , due to fact that the individual is just only there to make short-term profit, he or she may endup selling there's Bitcoin at loss because such individual are not long-term investors..

But as a long term investor who started his accumulation using Dca strategy to keep accumulating some Bitcoin for long-term holding, would have more chances to accumulate some large quantities of Bitcoin with lump-summing irrespective of his financial capability. Mostly when the price is low with his reserve funds. But in a scenario such user found he or her self using the lump-summing strategy when bitcoin price is high (as increased) and lateron began to dip massively, such user won't experience any fear that would lead to he or she selling at loss because their mindset as already being fixed for long-term investment In Bitcoin. All such individual would have to do is to keep accumulating using DCAing strategy.