I don't completely agree with you on this. Limiting Bitcoin savings to "discretionary income" seems like a good idea, but it doesn't take into account how wealth is actually made. People that were able to save a lot of money didn't wait until they had money left over after spending it; they put Bitcoin at the top of their list of savings, insurance, or retirement accounts. If you simply buy with what's left over at the end of the month, you probably won't ever have a big position.
I don’t get your point mate. Are you saying that one shouldn't only invest with his extra funds after taking care of his monthly expenses and basic needs. That's the right money that you should use to invest into bitcoin which is your discretionary income. If you go and invest beyond your discretionary income, you are not investing but gambling because when your needs arises, you will sell those bitcoin that you bought at loss if the price is dip below your entry point.
It's not by the amount that you are using to buy bitcoin but by how consistent and persistent that you can keep your bitcoin journey ongoing for 4-10 years and above is what really matters a lot and that should be your priority when you have started your bitcoin investment and have built up your backup funds.
When you have started your bitcoin investment and you want to increase the amount of bitcoin that you are buying weekly, you should trim down your expenses and look for a second means of income in order for you to increase your discretionary income so that you can invest aggressively within your discretionary income.
Wealth is built gradually and not in one day which the DCA method has given room for the pleb to buy bitcoin gradually and build up wealth overtime with their steady bitcoin purchase every week. There's power in little beginning and little piling up before you know it, you will be surprised with the size of your portfolio in future.