Yes, and no. As OP points out, in order to optimize, there must be something to measure. This is Google saying the benchmark is what they'll be using as a meas

Yes, and no. As OP points out, in order to optimize, there must be something to measure. This is Google saying the benchmark is what they'll be using as a measuring stick internally (and likely, in their marketing against competing browsers). Does all of this make the benchmark a useful tool for Google? Yes. Is it the best benchmark for cross-browser comparison? Probably not.