Lets have a little look at the DMG and some 5e Modules, should we?
DMG on building encounters:
The preceding guidelines assume that you have a party consisting of three to five adventurers.
3-5, okay... we could just take the average I guess. What would that be? Ah right: 4.
And now some Modules:
Lost Mine of Phandelver: "...adventure for four to five characters..."
Hoard of the Dragon Queen: "The ideal party size is four characters."
Rise of Tiamat: "Four characters is the ideal party size."
Curse of Strahd: "...for a party of four to six characters..."
Storm King's Thunder: "adventure for four to six player characters"
Is there any number, that seems to be coming up more than others?
So stop blaming DOS2, just to have some cheap shot arguments. The more probable thing is that DOS2 has only 4 PCs, due to Larian wanting to get the BG3 licence from WOTC.
