There are obviously plenty of people who are “fine” with it because they don’t know that there was a “previous” and as you say, won’t come on here to comment.
That doesn’t mean they wouldn’t advocate for 6 or any other X number if one bothered to ask.
Is it nostalgia because what… it’s been 20 years between BG2 and BG3, the fact remains 1&2 had a certain party size and this one is different. It’s a change. Is it a better one? That depends on your own point of view, but given the threads on here I will say with confidence that the majority on this forum, given the option, would appear to prefer 6 over 4.
As for the wider world, no, none of us can say, not even you. We can only extrapolate, but that of course brings statistical bias.
