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.
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.
The challenge with seeking the bottom is that there is no technique that is accurate in predicting what the bottom is. If you remember, just few months ago Bitcoin price was stuck around $29k qwhich made many people assumed that was the bottom. Many bottom seekers went long in line with what you have said. Little did they know that price will dip lower to even below $25k thereby proving once again how difficult it is to determine the bottom.
I was actually tempted to go all in that period before I learnt DCA and setting limit orders following conversation in this thread and WO. I have to spread my position to lower prices and when the dip finally happened, most of those positions triggered at lower prices thereby giving me more Bitcoin than I would have gotten.
Now I apply the DCA completely and I hardly pay attention to the price, the dips, news or whatever... I just buy the amount set aside for Bitcoin. This truly brought a whole different feeling and peace.
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.
I can tell you for a fact that the DCA method is always a good strategy irrespective of the market condition. The advantages far outweighs any disadvantage you might envisage. Just know why you are buying Bitcoin and allow DCA help you achieve your target with less worries.