Your argument is legitimate. We don't know the exact mechanisms by which Google enacts their affirmative action hiring policy. We don't know if it's through quotas or scores or anything else. An affirmative action hiring policy, though, is built to hire more of a minority in some way or another. When the pool of workers of that minority is quite low(like in tech), I don't see how an organization can have such a diverse workforce without at some point choosing a weaker candidate that happens to be diverse.

If this isn't the case and Google does actually hire people based on their skill and not skin color or gender, then Google needs to emphasize that, or else the majority of people will look upon women and such as "diversity hires" and build a disdain for them, thus hurting the cause.