Both partial or investing one time is a good way to invest in Bitcoin because not everybody can be disciplined enough to keep to investing partially. Some people are not good with money that they will use the money for something different than what they kept the money for therefore when someone with this type of habit has money to buy Bitcoin, they can go ahead and buy as much Bitcoin that their money can get them. The decisions we take today will be our saviour tomorrow because Bitcoin is not going anyway but it will be with us for a very long time. There are many ways to succeed with Bitcoin and buying them to hodl is the best way without having any specific way to buy Bitcoin. Many people choose to invest partially because it reduces the stress.
When investors are discussing or suggesting the idea of buying dips or DCA it is not necessarily for someone who actually has all the funds at hand because just has you have said they might take the funds and use it on something else or even leaving the money in fiat would just be making the money worthless because of the inflation that affects the fiat currencies, so when any intending investor has large money and doesn’t fancy DCA he should simply go for the one time purchase, because it is actually just the same as long as you’re holding for a very long time the profit is almost certain based on the past history.
DCA most importantly is for income earners who do not have larger capital to actually buy everything at once, the difference is just that at different rates of purchase you can have better price average than buying at once