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.