IMHO The debate about a bigger Party is important when thers a decision about having one implemented in future allready. That seems not the case sfaik.
Try to change the deabte about the iteration/ Variationproblems which will come into gameplay, when you want more and more characters which all need background storys, behavior etc etc etc. All those small details which hugley change the experience of the game. Every difference in a character needs another interaction and what not.
The more Characters you have to support with full backgroundstory and all it includes storywide until end of game is making the development of BG3 an endless story.
It takes a lot of writing time and then corrections etc. Its taking a lot, and i say alot of time to make it propper and not generical story stuff.
You want believable storys and interaction in this game between all characters, events, dialogs, encounters and so forth... Then switch to this debate how to achieve it.
Because all else you can have allready in other games not so focused on Story, Dialog, believable interaction etc. BG3 is more like a good Book in the way of trying to stay at a good compromise in storythreads by not having too many characters in the story.
More quality over quantity is key in BG3
I want to see the game beeing released at the and of 21 or mid 22 the least. Bigger party pushes this Date much more into the future or it stays but then with cut content or less defined Backgrounds, reactions everything which is allready in game for the 4 people party and works great, wont be working the same for a 6 - character party. When you want it done in the same developement time.
My understanding from the early discussions Larian had on this topic is that this is definitely one of the reasons why 4 is their current ORIGIN limit. It has been said that other NPC's might be able to join the party, you just won't have the level of interaction as you do with the core. So IF THAT IS THE CASE the discussion becomes about "Interaction & Dynamic" vs "Party composition". Do I value the interaction of 6 characters within a group higher than or equal to simple skillsets of the party, or am I more concerned of having a balanced party and the dynamic is secondary.
The argument will be BG1&2 had both, though of course the interaction elements of talking to your party were "limited" to text. The cinematic aspect of this iteration means that adding in 6 Origin characters worth of interaction from Acts 1 -> END is perhaps a hurdle Larian aren't willing to jump, but it is still a debate we can have in a discussion forum. What is it we would prefer (if given the choice), and to a large degree that is what has happened already here. And yes we are repeating ourselves to, but that is the nature of a large thread within a discussion forum.
So it boils back down to:
A - Party of 5/6 with full interaction and story across all members B - Party of 5/6 with partial interaction with characters outside the core 4 (i.e. hire mercenaries to fill slots) C - Party of 4 with full interaction (as currently) D - Other (there's always room in discussions for "Other")
One can always take fewer characters into your party if you prefer, so saying "I don't want 6 because I like 4", shouldn't mean we shouldn't ask for more party members, for me it's understanding what do we want, where would we compromise (if at all), and then what does Larian think or plan? Me. i am happiest with Option A, fine with Option B. so be it on Option C.