It’s not really a fair comparison because Solasta built their game engine to run 5th edition d&d. Larian built their game engine to run DOS2 and they are now just hacking in (some) d&d rules and things
Solasta had a fraction of budget and staff that BG3 has and by Larian’s account the engine have been heavily modified for BG3. BG3 perhaps couldn’t use same solution that Solasta did (like cube map design) but frankly any limitation that BG3 engine has is by choice, not by necessity.
Exactly. When Larian released DOS2, Swen and the upper management already knew that BG3 was their next project. Then they revised engine (I think they are now at Divinity Engine 4, or something like that). And
then they started developing BG3 with it.
So if there are things (DnD things or basic and general video game things) that the engine cannot handle, it's mostly by choice. Larian either decided very early that this feature X won't be feasible (e.g. looking at the sky, for the sake of giving an example), or they did not anticipate that they would need it.