Honestly, I don't really know nor care if Dark Alliance will be good. Perhaps it will be a great action game (I think thats what it is going for) and perhaps it will be terrible, but I don't think it'd have any bearing on BG3 because other than the connection to D&D they are two completely different beasts and I don't think would impact eachother's development unless they contradicted themselves in canon which would give BG3 some minor rewriting at most (unless Dark Alliance does something stupid like Blow up the entirety of Baldurs Gate.)