What you miss with raw Debian compared to TrueNAS is compatibility. TrueNAS makes sure that all pieces are compatible with one another so that when you update each piece or OS, the storage doesn’t break. The whole package is tested throughly before release.
Also, TrueNAS makes setup painless: users, permissions, shares, vdevs, ZFS tuning, nice dashboard etc. With Debian, you get a lot of config files and ansible playbooks that become hard to manage.
Ideally you won’t run other stuff on a NAS, outside Docker.
There's been a movement in the industry to bring storage back onto servers. They use the fancy buzz term of "hyper convergence" now though.
I will definitely argue that TrueNAS gives stability and ease of management. Some of that can be found with Proxmox too though. I think it just really depends on which medium you prefer. Perhaps trying both is the best option?
I’d try both, they tend to target different use cases. Proxmox doesn’t come with a lot of the tooling for things like SMB, LDAP, etc that Truenas ships with but you may find you don’t actually want any of these extras. In that case Proxmox would be a better choice IMO since it’s Debian based and a bit more streamlined.
Also, TrueNAS makes setup painless: users, permissions, shares, vdevs, ZFS tuning, nice dashboard etc. With Debian, you get a lot of config files and ansible playbooks that become hard to manage.
Ideally you won’t run other stuff on a NAS, outside Docker.