I dont think this makes any sense at all. There is no fixed resource requirements in any of your VM's ... ALL of them can make use of having more resources when they need it. Thats why probably the Proxmox (or Linux Kernel Developers, or Android developers) spend a LOT OF TIME thinking about governing resources. It makes no sense that an idling OS is sitting on a reservee core when your 25 Containers would need to do stuff in parallel.
I think you should resource the overall concept of your setup.