Laying off randomly and not low performers is par for the course for the management of Google. High performers will leave when the market gets Better and the company will fill itself with more shitty performers.
This is not how a top tier company behaves.
Low performers? By what metric? And your metric sucks, that's because a single metric is meaningless, even 10 metrics are useless.
Did you do over 200 CLs a year? 10000 LoC? 10-20 design docs? 10 product launches? CL comments, reviews, bug fixed, filed?
Sure you can identify outliers, but the baseline is not exactly very telling.
In my other companies layoffs were always random.
So yes, it doesn't matter which metric you want to use, but use something that is directionally correct with being a low performer, and get rid of those people. You might get some wrong but for the most part, people will be happier that the coasters and stragglers are gone.