Bitcoin is a volatile asset and so there's no guarantee that you will get 2x or above that amount from your investment at the end of the year. Realistically, thier might be years when we are not all that profitable with our investment and Bitcoin might remain at a certain range of price for a long time during some years before we tend to see anything close to 2×, 3× or so as you may have it.
That's basically the whole essence of long term investment and the application of the DCA methord in doing so because while you're investing for the long term, even when you don't see yourself in a good profit at certain time, you just take it as an opportunity of buying more Bitcoin and to continue doing your DCA till you reach your accumilation goal.
I agree with you that using the DCA method to accumulate Bitcoin does not guarantee that we will be getting two times our investment at the end of the year because Bitcoin prices can stay stable for several months. The DCA method is easy to understand, but it is dependent on the amount of money and how the individual wishes to invest. However, some individuals who invest using DCA methods, invest once a week, whereas some buy once a month, however, it's necessary to understand that the DCA method is always profitable for long-term investors.
Furthermore, using the DCA method requires an ongoing strategy where buyers are not bothered by the changing price of Bitcoin and continue to accumulate for a long time because the specific purpose of using the DCA method is that you can buy at a high price and buy at a low price for a long time until the investors become successful with their investment.