As I understand it, I think they're disagreeing like this:
Blank: The valley used to invest in hard problems that made the world a better place. Now that era is gone for good. Because social media makes so much money, no one will ever want to invest in hard problems in comparison.
Grellas: Yes we are no longer investing in hard problems. But that era isn't gone for good. Because the valley is such a good place for innovative startups, eventually, startups will start solving hard problems again.
Blank: The valley used to invest in hard problems that made the world a better place. Now that era is gone for good. Because social media makes so much money, no one will ever want to invest in hard problems in comparison.
Grellas: Yes we are no longer investing in hard problems. But that era isn't gone for good. Because the valley is such a good place for innovative startups, eventually, startups will start solving hard problems again.