Let's look at different perspective.
G2 is good enough on Dust2, doesn't mean that they have to pick Dust2 every time, legends team such as Astralis, Liquid, FaZe and others know that Dust2 is the best map for G2. In order to defeat a legends team, you need to pick on the best map that your enemy loves to pick. If you are best in Dust2, I need to work more on Dust2, so in other maps that you are weak, I can beat you easily because in Dust2 although you played well but I won.
So, in my opinion, they should focus on other maps, seldomly pick Dust2. Because Dust2 can be a "secret weapon" when they go against legends team like Astralis, they just need to be consistent, and seldomly pick Dust2, and probably it may work.
I hope you understand what I mean XD