Larian created meaty characters, well written (imo). They've shown their personalities and some their secrets . All are difficult nuts to crack. Two more in the party won't add anything except slow down combat even more. Besides, I'm starting to hear banter between them ( recent patches added the banter?). Plus, one of the characters I swapped in is hitting on the girls. Amusing... my dialogue options need to be updated stat.. (lol).
I've seen some people say this regarding the companions in BG3 being well written and have secrets and whatnot (imo they're not. they're pretty generic and uninteresting with some being terribly written and just sound overly exaggerated and forced. Gale is the saving grace so far, but not by much) and use this as an argument for why 4 people in the party is the right amount. Now, not to say that you can't enjoy what you're seeing in BG3 regarding the companions, but this really makes me feel like you haven't played a game that really did this properly. For instance, I'dd wager you never played the originals. You certainly haven't met Edwin, Korgan, Minsc, Keldorn, Jan, etc. Characters in BG2 had SO MUCH more depth and flavour than the ones seen here. Their writing and voice acting is so many times better than here... And guess what, they were absolutely amazing in BG2, especially in a 6 man party.
As to "slowing down the combat"... I've talked about this in other threads already but this is so wrong that it pains me how it's not immediately obvious to everyone. More companions would not only increase the pace of the combat encounters since you'dd have more tools at your disposal to deal with the opposition as well as make it much more interactive as you would have more turns per round due to more characters to play. Take for instance the fight against the Kuo-toa, or any other fight vs a significant number of goblins.. It feels like ages until I can do something in the fight again. Having to suffer through the time those buggers take throughout their turns becomes boring after some time, especially because they're meaningless trivial fights without any risk or difficulty. Most of those fights I thanked my lucky stars for having two monitors, as I did my turn and then could watch something else in the other monitor while the AI tries to do something. If people feel combat is slow (which it is) it is due to the nature of making this a turn-based game. In DOS turn based made sense since any one of your characters could do a bunch of actions in a single turn and had almost free movement skills that covered the entire battlefield. I feel it is not really suited for a DnD computer game since there really isn't a lot a character can do in a turn so you spend most of your time waiting for the AI to finish their stuff.
Someone also mentioned as an argument vs 6 man parties the fact that it would include more micro-management. I mean... I don't even really know how to respond to this as I feel this is just completely silly (for lack of a better word). You're complaining that you don't like having to do actions during your turns or that you want to have the minimum number of turns possible in a game like this where the whole point of these games is the complexity they have and the things you can do. By that logic let's just turn this into a clicker game where it plays by itself and you collect the coins. Fuck it, let's just make the max party size = 1, hey, it's less micro-management!
What you don't get my man is that all these ppl just want a watered down version of D&D which is precisely why Larian went for 5e in the first place. In other words they really just wanted D:OS3 instead of what we have atm. So you could say we even got lucky.