I think our accumulation should be based on the duration of our investment not by reaching a particular amount target for those who are using DCA. That means if the duration is 5 years, you will keep accumulating that percentage until the maturity date. Setting a fixed amount is good but most persons will likely stop investing once they reach there target. Lets not forget that the more Bitcoin we have the more profit we will get in the future.
I agree with everything that you said but don't you look from this point that if you are using timeline to as your accumulation focus instead of bitcoin target, it might make that investor be whimpish in his bitcoin accumulation strategy and not invest aggressively, because he feels that he still have enough time to invest. Also since we are to invest with our discretionary income, nobody knows the financial challenges one might pass through during the process of accumulation.
However, if you are using a target that will make you strive to make sure that you do everything possible to keep your bitcoin buying ongoing with persistent and consistent overtime because you really have a target to meet. This will even make you mors serious to look for other means of which your can improve your financial situation so that you can invest in bitcoin aggressively. In every production company, there's always a target per day which will make them know if they did well today or not based on the target.
If you want to save to buy something of value, you will have an amount that you will target which when you have saved up to that amount, you can use it to buy the valuable. Bitcoin investment is even better than such valuables. You can set a target that you might never accumulate throughout your accumulation journey but reach close to such target. My target is currently 4btc which I may be able to accumulate in future or not but I just keep on working on how to achieve it with my regular DCA weekly buying and lump sum.