Ash, your BG1 and 2 experience is not a story that isn't about Charname but simply one that cannot reflect properly on all the things that Charname could end up doing on their path towards their destiny. Even so, it is still a story about Charname and it will always be a story about Charname, even if it can be rendered a bit oncoherent by extreme behavior, and even if the crossover from BG1 to BG2 is a bit bumpy.

Yes, BG2 ends badly if you aggro your only path towards Spellhold. That's a bit hamfisted but then aggroing in that situation is a fairly silly move, so why not? What else can they really do to ensure that players understand that they have borked their game and must reload in order to actually continue the adventure?

I agree with quite a few of your criticisms regarding the story depth of BG1 and 2, but while the story was imperfect, at least it was my adventure about my character and their companions. And it could go a whole bunch of ways. Was I betrayed by the vampires or did I bargain with the thieves? Did I repay the thieves' trust in me by putting them to the sword the moment they were of no use to me (meaning when I was back from the Underdark), in the name of justice? Or was there perhaps some ulterior motive of finding good loot? Was I honest with merchants or did those potions of master thievery tempt me into being a city-wide crime wave? Did I save Aerie or did I murder that filthy ogre with the siren voice trick? Would I save Viconia or let her burn? Would I save Nalia's keep and then dump her or would I help her? Would Valygar unlock the sphere alive or dead?

Those were Charname's decisions about Charname's adventure. Most of it didn't matter in the end, granted, but how is Charname to know?

In BG3, the story is simply not about the player character. It does not tell a story about the grand adventure of Tav, it tells a story about some Larianites and maybe some casual nobody named Tav who plodded along with them. We are not playing our own adventure, we are playing Swen's adventure of the Larianites with the Weird Tadpoles using Swen's characters with Swen's backgrounds and Swen's pick of personalities and Swen's pick of goals. The Swenish Larianites are all protagonists and we can maybe add a support character to the story, if we really insist.