I mean it doesn't even make sense to me. ZM is the printer that produces afterlifes. Why does it look like a printer for mortal worlds instead? Why do afterlives need fauna, flora and entire ecologies? Shadowlands in general just fails to make Death otherworldly. It's just a different life instead.
I don't know about it not getting enough foreshadowing. I remember catching one of the Opulences with their entourage traveling in Oribos with one of the attendants discussing the sepulcher and being sushed. It was immediately obvious tha the Sepulcher would be important. I don't think they failed to foreshadow ZM. What they failed to do is tie it better to the story. Firim and his expedition should have been more than a journal and Ve'nari and the Korthian attendants should have joined us in Zereth Mortis instead of or at least together with the Covenants.