To buy bitcoin with a lump-sum strategy is not bad; you can even buy bitcoin at a low price with a lump-sum strategy. As you said, it is for the rich investor. Some investors can't be patient enough to accumulate the quantity of bitcoin they want with the DCA strategy, and they can decide to buy the quantity of bitcoin they want to hold at a time with a lump sum strategy.
DCA strategy is not only established for the poor but could also be use by anybody irrespective of their financial status weather poor or rich, however the only difference between the poor and the rich in terms of using DCA strategy is the amount they budget on accumulation basis, for instance someone that doesn't have much money could only focus on the amount he can afford maybe accumulate using $10 on a weekly basis while the rich could budget up to $100 or more on a weekly basis, so don't have the perception that DCA strategy is only for the poor because on the contrary it can be use by anyone, and perhaps that's the method so many rich people are currently using.
For example, if you buy $500 worth of bitcoins, you can divide it into five parts. If you buy dip then you can definitely save a lot of money. This is where your average will control the price, because adding your high price and low price to the normal price will come up with the purchase price of your Bitcoin price. So if you buy bitcoins in few steps you can definitely save the most on buying bitcoins and holding it for a long time is safest.
There is hardly any way to know if you are going to save money by splitting up your payment - however, you can spread out your own cashflow management if you are not sure about it, and also spread out your BTC buys if you are not sure about it, yet you are not going to save any money if you start to buy by splitting up your payment, and then the price continues to go up during the period that you are making each of your subsequent payments. In the case of the BTC price going up, you might have had been better off just buying the whole $500 at once, yet you do not know which way the BTC price is going to go.. and another part of tends to be that you might not be sure if you are going to have all of the $500 or that you are in a position to spend all of the $500 at once, even if you have it... so yeah, spreading it out does have the potential benefit of the BTC price going down, yet surely the BTC price is not necessarily going to go down.... so you have to make the calculation based on factors other than your believing that you know which way the BTC price is going to go... which more likely would be based on your own personal cashflow circumstances including income and expenses and perhaps even some of the inconsistencies that might relate to your own financial and/or psychological circumstances.
Yeah, this thread has some built in ideas about trying to consider the dip and perceiving some advantage regarding buying on the dip, if you get the sense that a dip is going to happen and if you can get some sense for how low the dip might go, but surely those kinds of identification issues could be helpful yet they are far from certain and sometimes not even very good practices to attempt to figure out, especially if you might happen to be someone who is fairly new to bitcoin and you are stacking sats, it might not matter very much if you buy bitcoin at $55k, $60k, $65k or $70k - even though surely if you have some ideas that you can buy it cheaper, then that is going to get you more BTC for the same quantity of dollars.. but then you are brought back again to not really knowing if the BTC price is going to go down further, stay the same or go up... and then if you get some ideas about where the BTC price might go, you also might not have any strong senses of the timelines, even if you might have some guesses (even educated guesses).