Buying Bitcoin all at once in large or large amounts is also not a problem for investors or companies who have a lot of money and I have also seen this in several investment companies that are very brave to do this, for example, like Blackrock and Microstrategy today where they very often buy Bitcoin in large quantities and the DCA they do is also in larger amounts rather than in smaller accumulations like investors who only have limited capital. However, what you need to understand here is that a strategy like DCA is not bad at all even though the amount of Bitcoin purchases can still vary greatly for each person because it is also always adjusted to our respective abilities.
These two companies mentioned by you have huge amount of money but they are adopting DCA in investment. Maybe this company has a lot of money with which they buy a lot of bitcoins at once but they are constantly buying Bitcoin. They sometimes buy more bitcoins and sometimes they buy less bitcoins. MicroStrategy has recently raised another two billion in capital to buy Bitcoin. They are currently buying small amounts of bitcoins but their goal is to buy bitcoins regularly.
Every investor should buy Bitcoin regularly and hold their investment for a long time, just as these companies regularly buy Bitcoin. Everyone should focus on buying bitcoin regularly to invest in bitcoin. If someone has the money to buy more bitcoins then he will buy more bitcoins and if someone has the money to buy less bitcoins then he will buy less bitcoins. Still he should buy bitcoins regularly.