This in incorrect, I have been at Google more then 5 years and the work has been in go. Most of the teams around me use go as well. But this is not to say that there is lesser java/cpp use.
You just happen to be in the subset / cluster / areas that write in golang. Probabilistically speaking across the entire Google engineering population both you and the teams around you are outliers. That doesn’t mean golang is insignificant.
As to whether golang was worth it I disagree with the parent, I think it was probably worth the resources invested, even if e.g. usage has leveled off internally, but at any rate this is a hard thing to measure so we’re all just opining.