I would not have minded a party lock. By the end of Act 1 the party could be a tightly knit group of heroes/monsters kept together by shared acts of bravery, villany, selflessness, greed, choices of "lesser evil" etc. that it does not wish to add have new members - as "none are worthy" or "are a security risk, not sharing the same atrocities" as the "in crowd".
But as actions have consequences - "play stuopid games, win stupid prizes" - Origins/Companions not wishing to pee on you if you were on fire due to what you did, or did not do, in Act 1, should limit the field anyway.
Wiping out the Tieflings and (non Shadow?) Druids should eliminate cooperation with Jaheira and Minsc - I'd be dissapointed if it didn't.
Just to be clear, I'm very much in favour of "soft" party limitations, such as companions leaving you when their approval hits rock bottom, you act in a way that severely conflicts with their principles or they come to blows with another party member for understandable reasons.
What I was really worried about was us getting the DOS2 treatment:
The game forcing us to pick 3 permanent companions because 4 is the max party size (without explicitly informing us we're even making such a choice in the first place), only to have the abandoned companions come back to haunt us later and accuse us of leaving them to die, which we did only due to an arbitrary mechanical limitation.
There is no narrative reason why no more than 4 adventurers should travel together at a time. It's a game mechanic, and that's fine. As far as the story is concerned, surely the camp is big enough for anyone who wants to stick around. I'm very glad Larian see it that way too.
