People who keep bringing up "balancing" seem to be intent on creating a strawman as their way of justifying denying people who want a bigger party. Not a single person on this thread who wants a party of six has ever asked for the game to be balanced for the bigger party size.
I mean, anyone can ask for an objectively flawed product, it wont change the fact that everyone and Larian will laugh at the suggestion.
It's only so flawe like Larian limits the gameplay possibilities or their framework conditions for improvements. Assuming Larian doesn't want to customize it for a bigger party size, that's their right. But they could also be clever and say party size of four is the highest difficulty, whoever plays with bigger party decreases the difficulty. Two issues solved with once. Of course, it's not quite that simple and a few adjustments will have to make it happen.
Examples: - change Shove to a full action 5e compliant (regulating inflationary use becomes more important when we have a larger party)
- improve pathing and usage with elevators, boats etc. pp.
- no hardcore limitation of selectable story paths (three routes to Moonrise Towers) --> Even if we are forced to choose one path for the story, let us explore the other two afterwards (bcs it reminds me slightly of the three paths in the third level of Durlags Tower or the two tunnels in Sendai's Enclave back at that time). more XP etc. pp. In the DnD-universe you should not go the limiting way, but the expanding way... Not in vain Big World mods for Baldur's Gate were created. But there have to be a compatible framework for this and Larian should stay modding friendly in advance without leaving elementary basics to the modders... That would not be fair and appreciative to the volunteer modding scene, if that is outsourced to them in advance, so to speak...
I consider a party size of at least five to be a core element of the basic game.