For any real production system you have to use terraform and their ilk to manage clusters, as you need to be spinning up and down dev/qa/prod clusters.
I don't know GCP though. In the past I've seen kube cluster archs which are very very fragile as they spin up. If that's the case with GCP I can see why you wouldn't do the above and rather hand hold their creation.
I would love if this happened in the real world, but for every well-architected automated cluster management setup I’ve seen using Terraform, Ansible, or even shell scripts and bubble gum, there are five that were hand-configured in the console and poorly (or not at all) documented, and might not be able to re-create without a substantial multi-day effort.
I don't know GCP though. In the past I've seen kube cluster archs which are very very fragile as they spin up. If that's the case with GCP I can see why you wouldn't do the above and rather hand hold their creation.