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.