Large investment usually should be done at once because not many people will have the money to always buy much at every dip, and as you said, buying at dip should be an advice for people that are buying little by little. Within 2 weeks ago, bitcoin has had about 3 dip, and even if its $2000 an investor has bought those times, I am sure by now, there would have been a climb of at least $400 on the investment.
This strategy is actually not for an investor, it works more for crypto traders that are always in the market most times to monitor the price of bitcoin and using analysis to trade their coin.
Hmm, there is true sense in your talk, one cannot keep buying every dip because of financial constraints, even right now, there are so many people that have heard of Bitcoin investment but still does not have any money to make move to buy the coin, and the one that has managed to buy at one point, struggled to do so, depending on the economy of the pocket.
We can only buy at every dip when we have money, but it is really worth it when one have the opportunity to do so, it will give one huge return on investment when the investment become very mature.