I believe that article is referring when you need to fetch the data in differents places. Of course in your design, a single SQL query to you database would resolve it, probably you would use the same query for a Graphql resolve. But when a field need to be fetched from another database or document in a nosql, for example, graphql tends to be more organized, of course in a restful APi you would run some concurrents jobs and have the same result. I believe that best benefits that I got from graphql is flexibility in the endpoint with some basic validation data type and a good structure in the backend. However, about performance is debatable.