I see plenty of discussion about CFAA being used against scrapers, particularly automated "bot" scrapers, but I don't see anything about alternative clients, where a human consumer of the service is barred from using the API. But I also only did cursory searching, so some sources for CFAA applied to API would be helpful.

I'm not sure how this would be any different than other software projects that use an API they don't own. Things like Cider for Apple Music, Ripcord for Slack, and the many Spotify clients all come to mind. Perhaps those are less aggressive in pursing 3rd party clients?