We cannot necessarily presume lump sum to even be an option, since sometimes people come to bitcoin an they don't already have cash available and/or they might not even have other investments from which they would be able to employ lump sums, so sometimes it does not even make sense to presume lump sum as an option when it is not automatically an option that normal people end up having and even if they were to have some lump sum potentiality, they would first have to designate such amount towards bitcoin investing, which might be an actual obstacle for some folks in which DCA makes more sense for them since they are not ready, willing or able to redesignate some lump sum amount that they might have towards bitcoin investing.
I really understand what you are saying but it is very important and for everyone to have a broader knowledge of various strategies as it being exhaustibly disscued here in terms of figuring out from what financial stratification you belong to, and for reference purposes. However, the lump sum buying are mostly practice by those in upper class and not for some middle or lower class where identifying your class gives you the preparedness in terms of making an informed decisions towards your investment plan, it pointless for anyone presuming lump sum to be an option when apparently you don't have what takes, everyone has to figure out the class where he or she belongs to in terms of choice of strategies, be it dca , lump sum and the rest of them, which will be a hedge over your planning working towards a successful Bitcoin investment.
Lump sum, DCA are strategies that can be used by any investor in terms of Bitcoin Investment. I won't associate social class to any form of investment, whereas we talk about it in terms of ability to be consistent in your accumulation phase.
For instance; An income earner of $3k monthly decides to begin his journey in Bitcoin and starts with $1500 which is 50% of his income, that lump summing probably later on he develops a plan in which he accounts $200 weekly. Any class can lump sum or DCA is just a matter of subjectivity. Just like sometime you can decide to add extra $$ to your weekly amount for accumulating Bitcoin just to increase your holdings.
In essence, everyone should have a plan, DCAing keeps us in a position of continual Investment same time you can lump sum too. Both works, it just a matter of discipline and consistency not exhausting yourself not social class or whatever.