Yeah, i need 5 or 6 size of group too, because 2 reasons.
Please forgive my english... far away from my natural language xD
1. Last i played Pathfinder:Kingmaker (size of group is 6 and loved the tactical options and the diversity in the group) and thougt that i can play D:OS2 but the size of group is horrible. Mage, Klerik, Fighter and a Rogue or Archer or a Archer with options for Lockpick ... i hate it. And than i have so many options for classes that i cant make a decision. (EDIT: Because of this, I deleted the game before escaping the island and will probably not continue to play it.) Here i have the same problem. Why i can chose from so many rasses and classes if i can play with 4 only in a group by 3 fix classes? Thats not funny. I like Wasteland 3 more than BG3 alone because the size of group.
2. and this is my fault too, i thought i order a BG3, after i played BG2 so mutch with this huge group ... but with a group of 4 i have not the feeling this is a BG. Okay, that was my expectation and I was disappointed. In short, if I had informed myself beforehand and had known that there are only groups of four, I would not have bought the game.
In this moment i get the 5. member i praied that the group is bigger than 4 and ... no. No good feeling.
I would not refund this game because i think thats would be great in future but this fault, dont collect information before i bought a game, i dont to that a second time...
Even if they don't add, wait for full release and then get the mod. They specifically said in some interview/panel that they left room for more because of how popular the mod for more party members was in Div OS2.