For every Larian, you have Bethesda, Bioware, Obsidan, etc, going more and more mainstream.
Yes, but it was also true back then, for every Bioware or Black Isle Studios, there were many mainstream shoot-em-up titles. And today, there are still many indies taking a risk at releasing something original and not easy on the player. Hades is not more "mainstream" than Bastion.
Owlcat Games is another good example. They could have stopped at the ruleset, especially since they quite delivered on that level, but they added an extra layer of kingdom management or crusade system, they've also added more classes and the mythic paths in their 2nd game.
Once they get big and a lot of money is involved, sure, companies are taking fewer risks, especially if they've become part of a larger group. But others take their place, or at least I like to hope so
That said, I don't agree with the "more open" part. Their more recent games aren't really that open imo. You can technically travel in most directions, but areas are level-gated. I'm not including BG3 when I say that since I've only seen the first map.
I mean with the general freedom it offers to the player, in the story, in combat, with the objects and NPCs. A little on the map, where everything is on the same big map but there are chapter gates, you're right. I'm not sure about the map, and I can't really argue it offers more or less complexity for the player. It's easier to get lost, but not with the map and its pointers, or the directions on the compass, the game just won't allow you get lost (I'm 100% with you there).
In what way? I don't consider having fewer skills/abilities or being guided right to my objective a shift in complexity.
The C&C, or the length and complexity of the story, for example. I don't like being guided, but not having to craft potions in favour of spending more time on the story or mini-games is a valid option for me. And to others, being guided may allow them to spend time on longer quests.