This was the main reason none of the various "spiritual successors" to BG ever really lived up. In NWN you just had henchmen and that blew. In Dragon Age you only had 4, but it didn't matter cause it wasn't really D&D anyway and they only had a few core classes there. Skyrim back to henchmen concept. Pillars, sure, but again not D&D. Everyone always drops the ball on this one.
6 is the magic number for this game Full party combat D&D setting Faerun
I'd hazard that's what everyone from my gen has wanted since Neverwinter, but somehow one of those planks hasn't made the final cut in any iteration since Icewind Dale. Its baffling
ps. when its built around 6 you have a simple way to scale up the difficulty quickly for players that want a more hardcore playthrough, since they could play with just a party of 3 or 4 and still get all the enjoyment of trying to strategize their way through combats with a smaller crew that way. I don't see how it lengthens combat with more companions or anything of that sort. Its just a matter of how they choose to scale the combat difficulty. If you build it for a party of 4, then going to 5 or 6 is a pain in the ass after the fact. If you build it for 6, then going down to 4 or 5 feels like monster mode and is fun. Nobody is ever going to grumble that its not a party of 7 hehe. It also makes replay more appealing too, if you want to try and solo and the like with a higher lvl character. Or try things out with a B team roster. All things that make me think of the BG model
pps. the 6 person party in BG was a call back to earlier games from the late 80s into the 90s like Might and Magic III and Xeen or Eye of the Beholder and Pools of Radiance, and that's one of the reasons it was so rad when BG dropped originally. There's just a feel to the full party of 6 that makes it all more Epic.
Like a legit legendary book of artifacts level campaign. You hit the big time when you need 6 to pull it off lol. That's all I'm saying. Don't settle for 5, go the for the Dragon's Orb!!! 6