I company I worked at had 20 or so sites on a headless API based CMS. Basically you’d enter structured data in their proprietary backend, and the site would request that data as JSON via the API. The marketing department hated it with a passion, because there was no way to do “one-off” things without involving IT, and IT hated it because marketing needed permanent handholding for the simplest of things.

After about a year of paying €8000 a month for hosting they replaced it with one really good 100% custom WordPress theme.