OIDC integration, RBAC, data persistence/replication across nodes, observability, mTLS.

And yes, you're right, all these things are complex in any situation, except when you simply use a load balancer and two servers. There are companies estimated to be worth close to US$2B using with sub 30 servers using a service you may have heard of: Stack Overflow (https://nickcraver.com/blog/2016/03/29/stack-overflow-the-ha... && https://nickcraver.com/blog/2016/05/03/stack-overflow-how-we...).

(As an aside: K8s does not free you from your Cloud vendor - after floating around my city working on various "platforms", all locked in due to IAM, for example.)