It's not the manifests so much as the mountain of infra underlying it. k8s is an amazing abstraction over dynamic infra resources, but if your infra is fairly static then you're introducing a lot of infra complexity for not a ton of gain.

The network is complicated by the overlay network, so "normal" troubleshooting tools aren't super helpful. Storage is complicated by k8s wanting to fling pods around so you need networked storage (or to pin the pods, which removes almost all of k8s' value). Databases are annoying on k8s without networked storage, so you usually run them outside the cluster and now you have to manage bare metal and k8s resources.

The manifests are largely fine, outside of some of the more abnormal resources like setting up the nginx ingress with certs.