I think what he is trying to say is that those who buy with lump sum and those who buy with DCA will end up making profit in their investments on the long term. What really matters is the size of investment at the end of the day. He is not say that they will have the same level of profit from their various investments. But it's also very possible that the person buying through DCA might end up making more profit. Bitcoin might dip more than the price you bought with your lump sum and remain there for many years while the person that is buying through DCA is continually buying before you know it he/she has acquired more bitcoin than your lump sum at different prices, some even cheaper than your lump sum buy entry point.
For my understanding if someone buys at once with all the money he has then there is a big potential in two contexts where if the price goes down after he has finished buying then he has no chance to buy in the Dips. And also if the price rises after they make a purchase, they will be more enthusiastic about investing in Bitcoin because they will immediately see the profits they get. Even though the investment they use is for the long term, I prefer to do it with DCA better than with a lump sum purchase.
Purchasing at once will usually have an impact on a person's psychology because he has already used all the money for the first purchase. and when the market situation changes suddenly, of course he will think of a thought about his first decision that seems as if he didn't have to make it. A thought arises that may not be ready for that moment which will certainly result in a wrong decision if he is unable to forget it. Apart from that, whether you buy it all at once or DCA, you will definitely get a profit in the end, the important thing is that they have the desire to keep Holding it.