This seems to go counter to modern practices, which is to not bother with content at all at the start, and to "find the fun" in a gray box level first.
https://www.retrogamer.net/profiles/developer/sid-meier/
> From a game design perspective, we established an iterative process in which we create a basic prototype that’s fun to play, even without exciting graphics and fully implemented features. We have a system, we play and then improve, then again we play and improve, but this is done throughout the development process. We keep what works and get rid of what doesn’t. This approach ensures that we remain focused on the gameplay experience every step of the way and deliver a fun game.
Figure out a fun mechanic and build a game around it. He even had a talk where he discussed several game prototypes that had mechanics he initially thought could be fun, but after implementing weren’t great so moved on to different projects [0].
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Deus ex is sort of that way. In deus ex it is the conversation engine. It was the first thing they made and is really the mechanic around which the game is built.