Different people have different strategies in terms of investment and everybody have a particular strategy that work for them.
Buying Bitcoin by DCA does not necessary mean that the investor have limited capital, most people that buy Bitcoin by DCA still have the capital for lump sum but one of the reason why some people prefer DCA to lump sum is that some people see lump sum as a method that is risky because of the volatile nature of Bitcoin which they cannot possible tell what the price may be in the future. So to avoid any uncertainty in regard to dip they see DCA as precautionary way of buying Bitcoin than lump sum which requires buying Bitcoin at once with the capital at hand without considering whether the price will dip or not.
The truth is that if an investor see's lump very risky because of the volatility of bitcoin I don't think the DCA method of investing will be seen in a different way because these are different strategies of investing but the same market. I do not agree with you why you think people don't prefer lump strategies because of the volatility of bitcoin, even in the DCA method volatility still happens. People just prefer to use DCA because it is straightforward and stress free. The most important aspect using the DCA method to invest is that you can be very consistent with your investment because you are just investing with amount you can afford, it doesn't matter what the amount is but the important thing is that one is investing with ease.
even though buying using the DCA method or doing lump sum is still going to be in the same market, the opinion he shared is actually true because a lot of people prefer the DCA method to the lump sum approach because it gives them the chance of investing gradually and somehow reduces the risk of lump summing at a very high rate and having to wait too long before expecting some sort of returns since for the most part, a lot of them are short term investors.
your thought on the other hand is equally valid because the same risk that comes with lump sum also comes with the DCA method and if you really consider it, if you have the means to lump sum and you are able to do that, you save yourself from being bothered about staying disciplined in consistent buying while using the DCA method since you only have to make one purchase at a time. as long as you can work with that, you can just wait till you are able to do or just buy at whatever time you have the means of buying while being less bothered because you already have some amount of bitcoin stack you are holding.
comparing lump summing to the use of the DCA sometimes looks like one is looking for excuses to give as to why one is not investing because at the end, we all know what we have in our hands and knows what strategy is suitable for us. whatever strategy you are able to adopt that gives you the best amount of returns and helps you get to your investment goal faster enough, then it is only best to stick to it rather than looking out for an ideal strategy that doesnnt even exist.