I am just here to say that I also very much approve of the idea increasing the party size.
And here is why:
I DOS2 (which I assume is the reason Larian went with a 4man party) all of the characters were class fluid. Story-wise, some roles might fit them better than others - but anybody could do anything, meaning you could choose your characters freely while not sacrificing your team composition. This meant you could without an issue choose whatever 3 characters you wanted, no matter their "prefered" roles. The player could focus on the roleplaying perspective and let their imagination justify the reason why someone like Ifan would be a mage, or Fane would be a fighter.
In BG3, however, all companions are tied to their classes and some even to their subclasses. This forces the player to do one of two things: A) pick their own class to suit the companions they desire to bring along (which is dreadful) or B) pass up on a character they might have wanted just because they don't fill their current group needs. An example of our current followers would be the difficulties of bringing both Wyll and Gale together, unless the PC is a front-liner.
OBVIOUSLY there are ways to play around this. I am most certain that people would/could successfully make a run with a PC-made wizard while bringing both Gale and Wyll and then ... Idk, Astarion. But it would make the game significantly harder and that is really unfortunate from a roleplaying perspective since we *are* limited by game mechanics to only 3 companions.
I mean it was 5 in demo version... When they first showed game in demo version, they had 5 companions in group. So for now, I don't understand why they changed party size to 4.