Agree with your opinion. This is also my understanding, please correct me if you think I'm wrong. When he said loss with DCA when the market goes up, you don't really lose, you just gain less than investing all at once. Likewise when the market goes down, you lose less than investing all at once. So, overall, DCA serves as a safety net to minimize losses, while limiting profits. The DCA method is more like value investing...
In this case, the price at which you start DCA is very important. And if you decide to start accumulating Bitcoins at the current price using the DCA method, then you will not need to be surprised that the price may decrease and your investment will have a negative balance.
DCA method can be started at anytime when a person is ready, it's your money and you have the freedom to start at anytime, it is the beauty of decentralization, the decision solely depends on you. But I can agree that there is a best time to start the DCA journey and that is during bear run when price has dumped so that your money can get you more value of Bitcoin, as price starts to increase so will the value of your Bitcoin will also be increasing. Unlike starting DCA method in this bull run when we are constantly seeing new ATH, it will not be profitable for a new investor to start now because anytime bear run will start and price will start to dip, which will depreciate the value of Bitcoin..