> I've seen some systems with a lot of pieces where teams have attempted to avoid repetition and arranged to use a single source of schema truth to generate various other parts automatically, and it was generally more brittle and harder to maintain due to different parts of the pipeline owned by different teams, and operated on different schedules.

I'm not sure what would lead to this setup. For years there are frameworks that support generating their own OpenAPI spec, and even API gateways that not only take that OpenAPI spec as input for their routing configuration but also support exporting it's own.