What I don't get is, some people are dismissing 4 man parties as fundamentally flawed because of its supposed limitations. Is there even a single 4 man parties CRPG out there that pleases those persons?
Not me. Even Dragon Age games, which I like very much, I would strongly prefer a 6-person party. And the reasons are very simple and the same for all games: 6 over 4 means I get to use more of the available companions actively, and to have more companion interractions, banter, roleplaying, and connections to the world.
I will say this: I don't mind having a party of four, what exasperates me is *having* to leave someone out of the party, for the reason you listed. Unless it is a stealthy mission, my brain cannot cope with why I shouldn't bring everyone with me.
But this is a problem I have with every single RPG, not only BG3 :P