This game is designed around a party of 4 players, and that is fine. To change it to 6 would require the developers to start over on a huge amount of design work.
I wish people could stop to make up shit as armchair developers to legitimate their bias.
This sounds like a case of the Pot calling the Kettle Black. You're accusing me of "armchair developing" while second guessing their decision to go with a party of 4 in the first place, and telling me how easy it would be to change it to 6. You don't know that. I'm sure they have very good reasons for choosing a 4-person party in their engine, and their story. And since we don't know their development process, we have no right to second guess their decision on this. On top of that, I would actually prefer a 6-person party, so don't go accusing me of making this point to "legitimate my bias". Because I'm looking past my personal bias to understand that I don't know the development process, so I'm giving them the benefit of the doubt that they know what they're doing. That's why I'm saying "stick with 4". To demand to the developers they change their game design to a 6 person party simply because we feel like it, and because BG1 & BG2 had a 6-person party is entitled, and selfish. Larian has proven that they know what their doing in this genre. It's their game, it's their art. Not ours. Let them create their game and their art in their own way. Judge a game for what it is, not for what it isn't.
I want a 5-6 (preferably 5) charcater party for a number of reasons, but I will say that this is very much the exact time to ask Larian to change the party size. Early access is here to see what works and what needs changing, and if Larian ultimately agree with the people that say the party size needs changing, then let them. If they think that it's not worth it to change the party size then it won't matter what we said. From what I understand Larian is more than capable of standing by their decisions, even ones they apparently later admit weren't the right decisions. They gave us early access because they wanted our feedback on what they were created. Furthermore just because it's their art doesn't mean their vision is automatically the best version of what it could be. More input combined with thoughtful consideration of that input is one of the best ways to create something great and I don't think we should automatically assume that their plan is the best plan; plenty of studio's who have created great games in the past have included stuff that on hindsight just didn't work as intended.
I just hope that if they keep the party size at only 4, they tune the combat down to a more manageable level because as it stands, the game's difficulty is such that a player with fairly average skill is painfully restricted by such a small party size.