Game AI and content generation in single-player games CAN be separated. For example, look at RimWorld – the graphical and spiritual successor to Dwarf Fortress. What Tynan and Tarn before him succeeded in doing was create the varied, ever-changing gameplay that one gets from multi-player and put it into a single player game. How? By letting the AI do the work. They didn't have to have an army of people writing the content because the content writes itself with the underpinnings of the AI systems.
In a slightly larger, more traditional sense, that's what I was working on with the Storybricks team on (cancelled) EverQuest Next, and then with PixelMage on (cancelled) Hero's Song… have the quests self-assemble and deliver to the player using the underpinnings of the AI systems. (See a trend here?)
What that gameplay does NOT satisfy, however, is a designer saying “but I want this story to happen for the player.” It's the difference between giving the player an experience and giving the player the experience.
