Every major problem with BG3 can be traced to the limitations of Larian's home-brew engine: cannot pause the game during real-time exploration; no day-night cycle; toilet-chain party movement; inability to do reactions properly; etc. Everything is because of the Larian engine's limitations.
Is it, though? What makes you think that if Larian were working with other engine, they wouldn't still design the game with multiplayer first in mind. Game with far smaller budget has stuff you mentioned - seems more like a design decision then an engine limitation.
