Downvoting is a form of feedback. If you are participating, then hopefully you are open to the idea that people could give you negative feedback. You can still participate, but if you keep participating in the same way, then I'm guessing you'll continue to get downvoted.

(I didn't downvote you)

No, but you need to be aware when you are defending your employer that you are obviously a biased participant in the conversation, and people will generally look at you as such. (Not disclosing where you work isn't a good idea either, it's blatantly obvious and easy to identify biased discussion members.)

And you therefore need to focus on things you can clearly demonstrate and/or prove. Which is good advice for all discussion, really, but especially when people are going to be evaluating your commentary with more skepticism.

If you know someone is wrong due to confidential data, there's a couple ways of tackling that. Saying you know they're wrong because of info they can't see is generally not a productive way to correct someone, because nobody can really be sure you're being honest, or see what you mean. You will change no opinions with that approach. However, you may be able to use public data to at least demonstrate that someone is probably wrong.

Quality of candidates and success of hiring practices tends to be pretty subjective, mind you, and it's going to be hard to provide hard evidence of it. Long term success of a company would probably be the best metric. (Of course, which Google has in spades.) Though the counter to that would be many of their more recent stumbles that show that trend may be coming to an end.

As an additional question, apart from the rest of my comment: You've said you're an SRE. Do you have a hand in hiring at Google, perhaps for a team under your management?

We expect and accept a high false-negative rate. Our commenting system is optimised for zero false-positives at the cost of many false-negatives. This is a deliberate choice. So yes, I would expect to see a significant dropout of commenters who are clearly qualified.

The sort of people that we want to comment are likely to come back for another try anyway, and the long-term effect of this process seems to be doing what it was supposed to.