Compared to what? If you're feeling really safe about the "internal-only" parts, just expose an endpoint to allow SQL (read) queries and you'll get essentially the same thing, especially if your data store already is SQL-like.

My first and last impression from GraphQL were that whoever wrote it hadn't had a chance to work with other query languages. A lot of the problems OP mentioned were quite on the surface. Had you ever used ORM, you'd be very intimately familiar with N+1 problem. Had you ever encountered SELinux, you'd be painstakingly familiar with authorization problems. Had you ever worked with XML (especially schemas), you'd be aware of parsing problems created by exploiting recursive properties of the grammar.

To me, GraphQL feels like a project by someone who is very enthusiastic, but lacks experience. If you need more examples of the same: the Terraform configuration language (not sure what it's called), Neo4j query language (I think it's called Cypher), libconfuse, Protobuf, and many, many more... unfortunately.