Jon, I love to see you making such a passionate case for freelance writers. Comments like that are gold for product teams, because it allows us to peak into the minds of people using the product. And I agree with you that Contentful is not necessarily the best solution for every single use case (though companies which struggled with development issues before tend to be ecstatic about having simple, reliable content API).
What I am personally wondering about is whether we reached the time and place where we can go from having CMS platforms with a convenient UI (think WP) to having intelligent CMS platforms (think AI applied to the process of writing). After all, our current technology already allows us to do things like automatic linking, contextual tagging, image filtering, similar content recommendations.
Why not pack these features into a CMS, so that writers spend less time manually re-entering tags, coming up with queries that give them the right set of images or making four clicks to link to a trending website. The CMS as we know it will not survive long, so exploring what comes next is definitely a topic worth investigating.