DCA method is typically made for people to be able to invest in bitcoin regardless of their financial strength and mostly for people who could barely have something left as discretionary funds because this method helps you buy and hold regardless of the price and condition of the market.
It seems to me that you don't understand what's discretionary income if not, you wouldn't say that people who DCA are the ones that barely have any discretionary income or maybe, I misunderstood you. However, anyone without a discretionary income cannot invest into bitcoin because you need a discretionary income in order for you to invest into bitcoin and hodli for long term, it doesn't matter if you have a steady income or not.
Anyone that invest with money that's not his discretionary income will end up selling his bitcoin at loss if the market is below his entry point because when he needs arises, he will have no option to sell his bitcoin.
In lump summing, more emphasis is placed on availability of large discretionary income and not just about having a steady cashflow.
You must not have a large discretionary income before you can lump sum. Anyone can lump sum provided he has extra money that he didn't plan for and has no important need for that money when he is given the money either at work as bonus or as gift in a wedding/birthday party or festive period. I can be on my regular DCA with my discretionary income weekly and I get a bonus at work or a traveling allowance of $150. I can choose to use all the money to lump sum or use half of it to buy bitcoin right away.
If you feel that you must have a large discretionary income before you can lump sum, you will end up missing some opportunities that you could have use those unexpected money to lump sum and increase your bitcoin portfolio faster.