For sure there are variations on strategies and even variations on personal circumstances, and of course if someone mostly lump sum bought bitcoin in 2015 then they could have paid anywhere between $200 and $300 per bitcoin, so let's just say that your friend got somewhere between 17 BTC and 24 BTC for his $5k.
I still consider the lump sum investor who sat on his investment for around 9 years to be a bit of a whimpy investor without enough confidence to keep buying bitcoin, even though some kind of a relatively whimpy approach to bitcoin investing still ended up paying off quite well for him.
I would suggest that if he had $5k to initially invest into bitcoin, he may well could have also had some kind of a DCA amount that he could have also continued to have had invested into bitcoin, such as $50 per week or something like that, so if he had continued to buy $50 per week of bitcoin for the past 9 years starting from August 22,2015 until today, he would have invested an additional $23,500 and he would have accumulated an additional 10.09 BTC, which surely would have had not been a bad place to be (even an improved place without necessarily costing too much to achieve it).
Surely the first purchases of $5k had allowed for the buying of much more BTC for a lower average cost than the later DCA amounts, yet the DCA still could supplement the initial purchase and put the guy in a much stronger financial situation.. which would have had been 27 to 34 BTC for a total purchase price of right around $28,500 invested.... but yeah people make their choices regarding how much bitcoin they might consider to be enough for their own financial, psychological and/or life circumstances.
Edited - added the below question:
Let's say that you were in your late 20s in 2015 and now in 2024, you are in your late 30s. Which one of the above two would you rather be?
Would you rather be the guy:
1) who spent $5k and had somewhere between 17 BTC and 24 BTC (with an average cost per BTC of between $200 and $300)
or
2) who spent $28,500 and had somewhere between 27 BTC and 34 BTC (with an average cost per BTC between $838 and $1,056)?
I would speculate that many of us would prefer to have ended up accumulating more BTC, even if our average cost per BTC might have ended up being higher within some of the scenarios as compared to other scenarios in which we had fewer BTC and also lower costs per BTC. In the above scenario, I am suggesting ONLY the addition of $50 per week of DCA, which surely should have had been in the grasp of someone who made a choice to lump sum invest around $5k.. I am not suggesting to gamble or to go out of our way in any kind of way to put stresses on our cashflow. Surely, I could have had come up with other scenarios in which the guy invested less than $5k lump sum and then reserved some of the money to DCA and buy on dips, yet we really don't know enough about the guy that DubemIfedigbo001n had presented to us.... including that surely it would have had been quite fortunate to start your bitcoin investment during a bottom period, which I believe most of 2015 would have subsequently been deemed to be a bottom period, even though when going through the period, there is really no way of completely knowing if the bottom is in or not.
To me short-term investment ain't encouraging at all the risk in it alone is too much compare to that of long-term investment. Like for instance someone that lacks the ability to be patient (because I believe short-term investors are really impatient) , and endup buying bitcoin at the peak and then a massive dip followed it , that individual won't have the mindset to keep buying and holding instead he or she will endup selling in loss because they lack the patient, thinking he or she has cut their losses.
But for those that are into long-term investment, instead of selling in loss they will continue to buy the dip , because they believe in a long run they will endup with the last laugh , so they will keep accumulating and holding , and if later on the price's endup risen (surging) they will endup with a far better profits.
Part of the dynamic that you describe I_Anime relates to position size too. A person who attempts to invest in lump sum and who does not have a plan to keep buying when the BTC price falls has put himself into a position in which he had not been prepared and he had overinvested, so it seems that anyone lump summing should be prepared to continue to buy if the BTC price moves against them (meaning down), and so they should already budget the possibility of a dip into their plans... otherwise they likely are not prepared, and the only other option in order to not fit the category of "overinvested" is to just plan to hold through the dip, which could take a while to play out, even several years.. so that could be problematic for anyone who had invested into something like bitcoin but did not have enough conviction to be able to hold through (including having in mind that the investment could go to zero...and to be prepared for such in terms of the amount that had initially been invested into bitcoin).