He started from the point of view that the current state is optimal in terms of outcomes for Google
No, he didn't. He was putting forth his opinion that the "current state" of Google's hiring practises were not optimal in terms of outcomes for Google, and gave logical, statistical, and scientifically-backed reasoning to support this position.
The tech industry has had decades of growth, profit, and innovation to show for its male-dominated culture. Google has a multi-billion-dollar multi-national mega-corporation to show for its male-dominated culture. So where is the comparable evidence that gender diversity would produce even better results than that? It seems to me that it's those who seek equal gender representation are the ones making assumptions.