I consider DCA to be way more flexible than you are making it out to be. You could have DCAs that are very aggressive and approach the use of 100% of your disposable income for buying BTC whenever the money comes in or you can make a weekly determination.
You could also set up DCA to be automatic and a very low number such as $10 per week (and maybe your disposable income is $1k per week, so you pick a real low and whimpy number such as $10 per week, or you could pick a more aggressive number. Of course the more aggressive you are, then the more careful you need to be that you don't overdo it and make mistakes and being more aggressive likely justifies having a more solid system of emergency and back up funds in place in order to rescue you if .you go to far in regards to your DCA or if you miscalculate and end up spending outside of your disposable income and from money you need for your expenses.
So small fund but for long-term strategy would really helpful as it is also risks management skill.
And We must not forget that-
"
Little drop of water,
Little grains of sand,
Make the mighty ocean,
And the pleasant land"
Yeah you are correct, the most important thing is for someone to decide that he wants to hold for a long term if you have that conviction of a long term holding then you can be patient and consistent in your accumulation, when I first started I looked at the price of Bitcoin and I said to myself when will i be able to accumulate a good amount of Bitcoin, but I saw an interview when someone said those who are buying Bitcoin at this price are buying it cheap compared to the future price, and I started accumulating little by little now I have gone a little bit far, I'm not looking at Bitcoin correct price I'm looking at it's future price if I continue with this consistency in my Accumulation then my future investment will be huge because Bitcoin is still growing and will keep growing.