^Buying Bitcoin with lump sum is the best strategy but the problem is not everyone can afford to dump at once which is why DCAing is very effective for accumulating Bitcoin even for the retailers. And also I wouldn't say selling at high is wrong because that's the basic of making profits by selling an asset while we can't really draw the line which is high and which is low due to the highly volatile nature so all we can do is just go with the instinct and try to make best out of it.
You can only describe something as best if that particular thing is convenient for everyone and has more advantage than the disadvantage, so saying lump sum is the best will be wrong because it is not convenient for everyone and everyone can not afford it and so the DCA still remain the best because everyone can use it to accumulate Bitcoin whether small or big and whether rich or poor. However, selling at high is not actually wrong that if you have hold for years and your investment is very matured but it is not right for low coiner to sell the little coin they have instead of thinking on how to accumulate more and any low coiner who sells when the price is high is obvious the person is a trader not an investor.
I agree with you on this facts about some suitability of investment strategy from my own perspective the DCA is concerned a more convenient and also know to be an accessible strategy to accumulate bitcoin it is allowed for any investment and at any financial capabilities are allowed it also suitable for everyone indifferent of your financial status.
Well the DCA over lump sum investing, such as reducing timing risk and it makes the investment more manageable for those with financial limitations.