It seems that the problem that GraphQL solves is Conway’s Law. For an org that can keep the backend and frontend together, it’s not much of an improvement.
I would argue that I've never seen even small teams keep the backend and frontend together if they are doing anything important. GraphQL is, if nothing else, a nice layer over your data that allows the backend developers to see what the front end developer are doing better than REST. That introspection is really helpful.