Even during the bear market, the best strategy to accumulate Bitcoin is using the DCA (Dollar-Cost Averaging) method. This is because, even in a bear market, the price of Bitcoin continues to increase and decrease. If someone decides to buy Bitcoin all at once because they see the price as low, it is and go futher to usees the money he did not supposed to use to buy bitcoin like it emergency funds is still possible for Bitcoin to drop even lower than the price at which they bought it. This could lead to panic, causing the person to sell and then try to wait for another dip.However, by using the DCA method buying weekly or monthly the investor accumulates Bitcoin at different price points. Anyone trying to "outsmart" the market might end up selling their Bitcoin prematurely.
It is also unwise to use emergency funds to buy Bitcoin simply because the price appears to have dipped. You can never be certain where the dip will stop before the price starts increasing again. Emergency funds should be reserved for actual emergencies since you never know when one might arise. If someone uses their emergency funds to buy Bitcoin and an unexpected problem occurs the following week especially if the price of Bitcoin drops further they could find themselves in financial trouble.
Yes, the idea of buying Bitcoin all at once is because the person wants to play wise with the market, and they believe that the price has dropped, they can take advantage of the chance to buy Bitcoin all at once, which will provide them with a big return when the price increase. Trying to deceive the market, the individual may be considered a gambler since nobody can tell if the price will fall below what they buy with all of their money because we can never predict the price of Bitcoin.
However, even though you have billions of money to spend all at once and whether you are rich or poor, the best option for investing in Bitcoin is to use the DCA method, which involves buying weekly or monthly, as you said. It is a bad idea to put all we have at once in the hopes that it would change our lives, this is very dangerous since we will have nothing left to use for other problems.
If they want to do that then I guess its still fine since somehow its good that they automatically have huge volume stored by buying huge volume of Bitcoin. Also somehow they intend to sell it in future so they might really get a great deal for doing that especially they bought their Bitcoin at very cheap price when the market dumps. Somehow lumpsum strategy is another good way to accumulate Bitcoin and for sure people could use this aside from their famous known DCA strategy.
But strategies will depends on the person since there are people out there can't monitor their investment all the time and cannot do DCA, doing lumpsum would provably good for busy type investors.