Buying at once seems more favorable for those who have bulk capital and have already made up their mind to invest same in Bitcoin. They don't see any need keeping those funds or employing DCA since the fund is readily available. This is not a bad strategy provided the intentions are to hold for long to be able to realize profits.
Yeah you have a point, for those who have enough funds that cannot be affected if using a bigger amount to buy Bitcoin can actually buy a higher amount of Bitcoin at a time and however DCA method may not be use for these kind of investment because the investor may already have more than enough money that could buy a whole lot of Bitcoin and still have many reserve funds waiting.
So irrespective of how important DCA strategy is, perhaps there are some kind of investment or accumulating patterns that may not require the need to DCA because sometimes due to the kind of funds we may have, we can decide to invest at once instead of buying bit by bit, so I believe that DCA strategy is based more on the people that has a low capital and that's managing to accumulate Bitcoin.
Lump sum buying is more of advantage when bitcoin price is at the bottom line of the dip, at this time, all you need to do is to buy once and just sit down and watch how the price starts going up again and your investment will also start increasing with the timeline. Apart from that time, the DCA method is still the most welcome strategy to use in buying bitcoin, this can also help you have plans on some other investment you want to diversify to.
The DCA method is not for only the low income earners, it is used by everyone, but the rich and the poor to accumulate bitcoin at regular interver to increase their bitcoin investment portfolio at ease, since they have the passion to keep on accumulating. Since it is very difficult to know when the dip will come, but if you buy at lump sum when the price of bitcoin is not at the dip, you will not be happy when the price begins to dip below the price that you bought, and that is where DCA come to play because you are buying regular irrespectively of the price of bitcoin at that moment.