I use Docker, Kubernetes (with Rancher) and some other container tools (but I'm not an expert, just a regular user).
So maybe let me try to comment, without making it a "religous" thing.
If I understood well, Since Docker joined the CNCF they split the project into a bunch of projects and docker itself, will focus on the daemon part while networking configuration and other parameters will be a relay to orchestrator such as Kubernetes.
Docker was the first container tool (all in one: container runtime, cli tool, orchestrator, registry, etc). Docker was challenged from many sides and there were even attempts to create alternative container "formats" (like rkt). And there were tools, like Kubernetes, that built on top Docker's container runtime.
Today, there's still "Docker" as the "one in all" tool (actually the upstream community project is now called Moby). But some parts have moved to other projects, most notably the container runtime "containerd" (with the lower level part called "runc") is derrived from Docker and Docker itself uses it (but not for everything, for example both "containerd" and "moby" have separate code to pull container images). And others have created their own container runtimes (for example Red Hat created cri-o (with the lover level part "crun"). Kubernetes itself originally used Docker as its runtime (and can still use Docker as its backend, which in turn uses containerd), but it's more common that Kubernetes distributions use containerd or cri-o these days.
Today for end users there are two notable standards:
- the container format that Docker established (now known as OCI) - all tools can use and work with it
- the Kubernetes API for container orchestration
Some people just use one of them (there are many use cases where you don't need complex orchestration - for example to build/test software in CI runners). Some are using both (for example to run complex web applications with Kubernetes).
The Kubernetes API is now also supported by VMWare (vsphere / esxi). A bit simplified: You can just point a Kubernetes yaml at your vsphere cluster. Under the hood vsphere sets up and runs VMs with vmware's Kubernetes distribution for you. This is roughly how I wished Kubernetes would be supported by Proxmox as well.
TL'DR: I agree that it wouldn't make too much sense to treat Docker containers as VMs (that's what LXC is better suited for). But IMHO it would be great if PVE could one-click deploy/extend/shrink a Kubernetes cluster for you, both control plane and worker nodes running as VMs. I recently had the chance to test VMWare's Kubernetes features and I think they're doing a lot right here. Their customers don't need to go to another vendor to get a Kubernetes distro (like Rancher) and painfully integrate it into their existing environment. They can just use it right away. And for VMWare it means their customers have a reason to stay and pay (even though there are great and more cost effective alternatives to vsphere, like PVE). (And don't get my praise for vmware wrong - I've been into vmware licensing at a large org and it wasn't fun. Really appreciate that PVE exists).
(Just my opinion as a user - I'm not an expert and there might be other opinions).