Lets take for instance, first week of last 2 month if someone purchased a bitcoin at a go without doing DCA don't you think such person could have made about 5 to 10 percent of their investment?
I quit agree with you, but the main purpose of DCAing is to for a shorting profit. Your absumption is base on some few weeks back. What about those who might have bough through DCA when the price of Bitcoin was dip at $15k earlier this year? I think they would as well make more than the %10 you are emphasising. It's only those who are trading, that are moved by short term profit while those who DCA are for long term profit.
person who is doing DCA may not have that profits because s/he ends up accumulating very little fraction of it.
Don't underestimate the power of little by little investment. If you have $10000 to invest at a go is up to you. But mind you most people find it hard to invest with the little money they make with there job. That is why they choose an investment plan that would not affect them. All hand are not equal. It is often said that "don't despise your days little begining". If for example some one who has a DCA plan some months back with a salary of $300 and decide to invest $30 per week that is $120 in a month multiply by 12 months that's $1300. So I think investment is decided on ones means of income.