Yes, I know. But you are assuming that this is a simple thing that can just be easily added without affecting anything else.
No, I'm not. I'm saying that it's something that it's absolutely worth to aim for with a full understanding of the amount of work needed for it (starting with a revamp of controls, which as I already said it's something already direly needed regardless of party expansion, and passing for a mild UI tweaking, which is still work in progress anyway).
And people are VASTLY overestimating the difficulty of "rebalancing encounters" with modern tools, to begin with.
That's quite literally the least of the challenges ahead, both because encounter design is still a a work in progress too and because "perfect balance" in encounters is a pipe dream, anyway. There will always be ways to break and even trivialize them, which is not even a real issue since doing so it's half of the fun at times.
I know many people don’t like that. But we don’t know what happens after act 1 and whether or not that makes sense.
It doesn't really matter. Whatever they have in mind, it's most likely a forced narrative device they are deliberately making happen with the purpose of that design goal. Consequently something that they could (should) reconsider on, if they wanted to, if they decide that the goal (namely "getting rid of the extra companions in one broad sweep") was questionable to begin with and managing an expanded party beyond who you are grouping with at a given moment can be far more gratifying.
Except if the game is designed to have 4 characters of equal importance
But let's be real, it's not. There will always be one main host and his partners as secondary characters like in the previous Larian titles. You can't ACTUALLY go "full competitive" against each other in these games, they always work just as far as there's some degree of cooperation between players and some agreement on who's in charge.