It's hard to convey tone in the forums. Very few, if any are losing their minds over this game.
I worked retail as a teenager so I am well aware of customers with issues. What you are seeing in the forums is nothing.
I will say this. Telling people, strangers, how they should react to what they consider bad news never goes well. It's pretty silly.
Pretty much this. Outside of that one thread with that questionable 'betrayal' wording, this forum is pretty tame compared to the likes of Reddit and Steam. And even then, this forum's perceived 'harshness' comes from a desire for the game to get better, rather than simply talking other people down for disagreeing and insulting them on a personal level for disagreeing with the 'developer's vision'. For some reason, people never seem to call out the latter (probably because it's usually a lot more dangerous to do so), even though it's just as harmful, if not even moreso because it's far more likely to lead to echo chamber behavior among the community at large.
Context is everything. One also needs to note that tone is not just something that a poster sets with their wording, but what everyone else chooses to assign to it too. For example, I would say the OP's use of 'they never promised' and 'it's your fault' to be considered hostile as well. At least from what I see on this forum, one side at least suggests changes and offers reasoning for them, while the other is quick to assign personal blame over a disagreement of preferences. After all, it's hard NOT to be hostile if you spend half an hour typing out a well reasoned response, only to get drive by posts like the below.
https://forums.larian.com/ubbthreads.php?ubb=showflat&Number=756875#Post756875Most of what you're reading isn't criticism, it's whining.
That said, there is also a certain questionable quality to not engaging with the debates directly and making a thread trying to tone police the forum instead, but again, I don't really know what context most of the posters in this thread are running off of.
Hardcore fans might not like it, but the bottom line is that the creators need to make enough money to warrant making these kinds of games. If you restrict the gameplay too much to absolute D&D 5e tabletop rules, there is a good chance that Larian will completely lose a huge number of their customers.
The point is that if Larian created a BG3 game that was a regurgitation of BG1 and 2, it wouldn't fly nearly as well as it is right now. The people who would buy are mostly those who simply adored BG1 and 2, and that would lock BG3 into a much smaller customer base.
While I am in general agreement with most of your post, the quoted part is an extremely bold generalized claim to make, and I am obligated to call this out. And I say this as someone who has never played BG1 and BG2. It is pointless to speculate on the popularity of something that didn't happen, especially with such a definitive tone, and some would interpret an attempt at that as rather insulting.
No one is able to accurately gauge the popularity of something. It's all perception. As someone who is actually aware of Larian's history before they made the D:OS games, they were pigenholed by their publishers into making action RPGs out of a belief that they'd be more popular, until Larian broke free and finally used Kickstarter to make enough money to make the turn-based games they always wanted to make.