I have no opinion on the former, but would beg to differ on the latter.
Gross' theory is that takes forever to prove that a person is a great investor. The right environment can make anyone look good for a long, long time.
The key in proving whether someone is a great investor is whether a person can adapt to change and profit in different environments.
Gross thinks that both he and Buffett have had big tailwinds at their backs for their entire careers.