My install is on Arch linux, I just installed incus and cockpit-machines and (from memory) that was enough.
But, yeah, it's definitely a step away from a full GUI...
But I think that's part of the appeal (to me)... there's a lot of things preinstalled with Proxmox, (and XCP-ng, etc), that I'll just never use... so if I could get that old Ras Pi3 as a 2nd node in the cluster without all the fluff... maybe that's a good thing?