When you are playing in rl then 4 players can do most things as players have unlimited minds. They can do anything they can think of and if they can surprise the DM they might even live through some of them.
Computer games are severely limited in that respect. For me 6 is better in a game like this as you get more playing options, instead of just tank, heal, trap, cast (or variations there of). With 4 you feel you are leaving things out of your party.
And as they have decided to call this BG3 and are selling the game as BG3 then it should at least be similar to BG1 and 2.
Its only a pity we don't have 2nd ed rules as well as a six man party.
Pretty much. That's precisely why "Pen & paper sessions are usually tuned for four players" is a bogus argument to bring to the table. Because they are two very different scenarios. In tabletop sessions four persons agree on how to build up a team from scratch and they are limited only by their imaginations on the way they can interact with each other. In a computer game you make up your party out of the limited options offered by a certain number of premade companions and their mutual interactions across the entire campaign are limited to a (more or less dynamic) handful of pre-established scenarios.
It's like arguing that in a RTS you shouldn't control more than a vehicle because in reality driving more than a car at once is almost impossible.