The DCA is a good method no doubt but the discussion is concerning using non discretionary funds and how bad it is for those who tend to invest and hold for long-term. Even though one use the DCA but with a fund that's not discretionary, I don't think such person would be consistent for very long since the funds meant for daily needs is at stake.
Therefore it's important to invest using the DCA for long-term purpose and to maintain consistency but more important to invest with that method using the discretionary funds so the investment would go smoothly for long-term as supposed.
The first thing you need to do before buying your first bitcoin is to check if you have discretionary income because it's only discretionary income that should be used to accumulate bitcoin. Anyone that buy bitcoin with money that is not his discretionary income is gambling because he will sell the bitcoin at loss when he needs arises and the market is below his entry price. There are some things that common sense is enough to let you know it's wrong.
This is why you need your discretionary income to start your bitcoin investment and a consistent discretionary income to continue DCAing consistent and persistent till you reach your bitcoin target. It's still your discretionary income that you will use to set up your emergency funds and other backup funds.
We all have pretty much the same idea of what we need to start investing. Basic knowledge, discretionary money, and a source of discretionary income. Basic knowledge requires us to have the knowledge to understand our position and the ability to determine how much it would be wise to buy at the beginning, the ability to buy Bitcoin, the ability to hold Bitcoin, the knowledge to create a self-custodial wallet, and the knowledge to store the seed phrase.
Although this may go against the opinions of others, I think an investor should take a few days to start investing. Since we are going to be involved in an investment for the long term, we may need to prepare ourselves mentally and try to make decisions as self-aware as possible without rushing. It is normal to make mistakes in the beginning, but care must be taken that the first mistake does not become the last mistake, that is, that no one develops a negative opinion about Bitcoin after an initial mistake. It is better to build trust in Bitcoin to start investing, so that if a mistake is made, it can only be described as a mistake.