There are some good NPCs out there: Halsin, many of the named female tieflings and a couple of the males, and Volo are all perfectly polite and some even nice. Something to keep in mind about your teamates is that they are all about to die and are in crippling pain on a regular basis. Regardless of any dark history, that level of stress, pain, and fear would make anyone cranky and standoffish.
I would say that most of the characters in the originals were pretty crappy at first too . BG1 barely had any interactions with your crew and BG2 had mostly sad/solemn/cranky options though you could eventually influence some of them to be less so. Of your starting companions, Imoen was the only one who hadn't lost a close loved one between games, and both of you were tortured endlessly by the opening dungeon.
I would say that there is a much better chance of influencing the characters in BG3 towards niceness and real companionship than there is in DOS2. I absolutely agree that almost everyone in that game is pretty much an a-hole. In DOS2 only a couple of the followers (and an NPC or two) seem kind, but they have their own tragedies to deal with as well.
