Investing in bitcoin needs to be tailored to each person needs. While DCA strategy can work well for some. Each person has their own financial goals and comfort level with risk and investment timeline. It is also important to remember that people can change their investment approach as they learn and become more confident. Your example of someone starting with DCA and then switching to lump sum investment after learning more is great example of this. At the end most important thing is to find investment strategy that works for each person and allows them to buy bitcoin at their own pace without putting their finances in danger.
Because in Bitcoin investment, methods such as DCA or lump sump, it is just a person's approach to how to invest in Bitcoin and how they can adjust it according to their financial condition and their confidence. In the long run they can change their approach to investing in Bitcoin, they can choose DCA or lump sump, whichever is free, the most important thing is how they set their finances so that they can invest regularly and not sell just for short-term profit.
A person is most likely to benefit the most if they invest in Bitcoin initially and keep it for a long time. The investor will be able to sustain his investment for a long time by diversifying little by little, which is why the DCA method is most important for both every holder and every investor.
I don't understand what you mean by diversify little by little, because from what I understand about the word diversify, it means to stop your bitcoin investment and put the funds that you are using to invest in bitcoin into another asset like stock, bond, gold or real estate.
A new investor shouldn't think of diversifying into other investment but rather he should stay focus on building ans growing his bitcoin portfolio overtime, because bitcoin investment is already outperforming other kind of investment both physical and digital in the market. Trying to diversify might make you lose focus and make thw wrong decisions that will lead to regrets. It is when you have accumulated more than enough Bitcoin and you feel you are not secured with only bitcoin, you can diversify into bonds, properties, cash equivalents and stocks.