I thing you are confusing not liking Larian design (which I am there with you), and the scale of what Larian is delivering.
The scale of what Larian is delivering isn't particularly noteworthy. Nor is it necessarily relevant to "A BG game"
Larian delivers a 3 Act story. With each act getting progressively shallower and less polished.
This isn't crazy outlandish design. This isn't some BG3 unique facet, this is not a pre-requisite for a BG game.
Most cRPG's have a 3 Act story. Some have more (Rogue Trader for example has 5 Acts over which its story is set)
The only difference is as a AAA developer, Larian can spend more time on the graphics so instead of being the typical isometric view with low poly models, they can use a more modern style of closer camera and high detail models (And spend money on motion capture to provide better animations). Which is all irrelevant fluff. It's not necessary for a game to feel "BG-like" it's not necessary to be a good game. It's just something that's a nice addition.
Yes, it is „just the first AAA cRPG”, but those dont appear from a thin air. You need tools, production pipeline, staff experienced with working with those tools and production set up making that type of game.
Yes. But it's not necessary for a game to be a AAA title in order to be good. In order to be a BG game. In order to be a successor in the series.
Would it be nice? For sure. But it's not a necessity. Not only that, but since the IP is controlled by WotC, any studio making a BG4 can be bankrolled to provide them with the tools and support (Provided they have innate experience with making RPG's. Which is likely unless we face another Golum type scenario where the IP rights go to some developers that literally have no experience at all)
I wonder how many publishers outside of Sven and his independent company would be willing to invest so heavily into such narrow genre.
Well, BG3's success makes the genre much less narrow. The fact that BG3 has won so many awards and sold so many copies directly highlights that the market is not necessarily as niche as it once was.
Publishers LOVE to jump on trends and when anything does well, it becomes a trend. (Like how everyone and their cat was making Battle Royales after Fortnite hit it big. Or how there have been a slew of Extraction Shooters after Tarkov's success, or going back further the vast number of MMO's created in the wake of World of Warcraft's success)
It's very likely that after the success of BG3, we will see more studios pushing for cRPG's trying to get their piece of the pie too. Of course the question is whether existing cRPG making studios will get funded and expand their abilities, or if publishers will pivot non-cRPG studios into the genre.
I would kill for AA-AAA Pillars of Eternity3 for example.
Unfortunately, PoE is in a particularly bad place right now. With Obsidian currently working on Avowed (As they wanted to branch out to a genre outside of cRPG), with also the company being at risk due to Microsoft's recent actions (They've been closing down studios left and right trying to recoup the money they spent on the ABK aquisition. With absurd actions like shutting down Tango Gameworks despite the success and awards of Hi-Fi Rush... So they can focus on making smaller, succeful games like Hi-Fi Rush...)