Comment by nitrogen

GraphQL is appealing from the frontend perspective, but I've yet to see a case where it would do anything but make the backend 10x harder to develop, and it doesn't solve the problem of the frontend also having to know all of the entity relationships. Since you're using Rails, it's a lot easier to just add a controller endpoint that provides the composite data (as has been mentioned elsewhere already) for one UI action/page/navigation/state change, instead of using an entity-focused API. Controllers are supposed to abstract over potentially multiple models, not just be 1:1 endpoints for each type of entity.