A little algebra can help us to find the difference (X) between BG3 and BG2. First, let's switch to a more common notation:
X = BG3 - BG2 --> X = (3 * BG) - (2 * BG)
Then some simple factoring will give us our answer:
X = (3-2) * BG X = (1) * BG X = BG
So, the difference between Baldur's Gate 3 and Baldur's Gate 2 is Baldur's Gate.
Except that, in BG 2, there was no Baldur's Gate?
Isn't that the point (my math is rusty)? If you subtract a game which doesn't have BG city from a game that does have BG city, BG city is the difference.
When one says the difference is the lack of something, that implies that one has it, while the other doesn't. At this point, neither has Baldur's Gate.