It’s rather difficult out to comment on the technical prowess of a game engine or indeed the software itself without a playable build to use as evidence. I won’t comment on Rockstar’s business because I don’t really care.
But it’s GTA. It’s the biggest brand in entertainment, period. They’ll sell 50m copies on launch day alone based on the fact that it says the three words ‘Grand Theft Auto’ on the box followed by a digit. GTA5 is so old now I rented it at launch from Blockbuster for the Xbox 360! Anticipation is off the scale.
Look at Cyberpunk 2077. Sold on the back of Witcher 3 it launched to a lot of hype as a bug-ridden mess. Fast forward 4 years and they’ve not only ironed out all the bugs but they’ve also relaunched the game and sold 25m copies as a result.