I think it's a testament to the writers' abilities that they got us to care for their characters so much that we feel hurt for them. I suspect the way Act III unfolded was out of their control. The game was in development for a long while and the studio was pressed for time.
Agree. I bought the game at the beginning of EA, so for me it didn't feel like a slap in the face at all, more like a slight let down after my play through: oh, game still isn't finished. I guess I have to wait another year.
Only that the time pressure is something that Larian is responsibility for. They set the scope of the project and the deadline, they should have a good idea about what they can handle and what not. And ultimately, if you publish a story driven crpg, make the story and the character interaction your priority (not the planned release date and not the percentage of players who do or do not chose to use the tadpole powers for example). Don't release it until both are satisfactory and sufficiently bug free (give your writers a veto right on that).
But as the things are now, Larian, just relax! We love your stuff. Take your time. Just make BG3 more stable with each patch, don't rush them. And eventually come up with a Definite Edition that provides a more satisfactory ending and adds some of the frequently requested stuff like more difficulty levels, custom party, QoL improvements, camera, DND implementation fixes...