There is a difference between using the same engine, and using the same EVERYTHING including plot transitions and the entire enironmental economy.
BG3 is a carbon copy of DOS2 with updated textures and lighting. They grafted whatever 5e rules would fit on their Divinity rules, and threw out the rest.
The ENTIRE STRUCTURE of BG3 is an exact 1:1 skin job of DOS2.
Out of interest, what exactly do you think an engine exactly is?
