Not sure how they can claim the world will be bigger than gta 4, san, andreas and red dead all combined. I mean san andreas alone was a whole state, and had 3 cities the size of los santos. GtA 5 is only one city ie los santos.
Unless they massively increased the size of their fictional city and the new los santos has no bearing on the los santos of san andreas. then i could buy it.
However looking at the map it , and its streets, it dont look to be bigger than the san andreas version of los santos, so no idea where they getting their figures.