Yeah, proxmox is debian. I think people don't realize you can install their fancy web UI on debian.

Proxmox is opinionated about how storage is allocated (I think lvm-thin is a bad idea), doesn't support docker, and has some quirks about getting the apt repos set up correctly if you're not a paying subscriber. It's fine if you want to use things in their opinionated way, but know that they're not doing any magic to make KVM work. KVM and LXC are the exact same as you'd get from debian out of the box.