Sandbox is probably more accurate than open world.
Sandbox has a different meaning and it's not even exclusive with "open world".
In fact, it just defines a specific flavor of it.
True. A lot of this is ultimately semantics as technology progresses and most AAA can be considered some form of 'open world'. When I think of open world--in the purest sense of the term--I think of something like Skyrim or Breath of the Wild, where you can basically go anywhere once the tutorial is complete and finish the game as quickly as you like. Sandbox is giving you the creativity to finish tasks/quests within a bound set of parameters. Most true open world games have sandbox elements but not all sandbox style games are true open world. Due to having an act structure, BG3 can't really be considered an orthodox open world game.
Where BG3 differs from a lot of hub worlds is that it connects several different biomes within the same map, while other hub worlds would have them separated to let them load in properly. Which also creates a sense of scale through non-diegetic elements.
No matter the fancies you wants for the story it won't ever be coherent with such a theme park map.
This map is only designed to enhance the gameplay at the expense of the story and the immersion into the world.
We have a saying in lit analysis circles that goes along these lines: "The film teaches you how to watch it." I think if the game does a better job teaching the theme park map and the way it functions within the quests and overarching narrative to the player, the immersion aspect won't be an issue. Or, at least, less of an issue, even for people who don't care for that type of design.
