Agreed. All I want is to manage OS windows the same way I manage Vim windows where the content and the container are decoupled. Surprised nobody has made this yet.
(But heck, with evil-mode maybe it'd feel pretty familiar?)
I think Hyperland or i3/Sway could also be scripted to behave this way.
I wonder how well this would work for a WM, though. Processes are a lot heavier than buffers so it kind of does matter how many are running. Unless it's a system like Android where any app expects to be oom killed at any time.
Doesnt seem super applicable to window managers at the moment, but there being a singular screen does seem like a severe UI limitation.