For super small applications, where you have 5-10 endpoints, you can say that GraphQL is an overkill. But imagine having 100s of REST endpoints and the client making numerous round trips to the server fetching loads of unnecessary data; GraphQL certainly wins in this case as you can fetch everything and exactly everything in a single API call.

[Edit] Also, the GraphQL spec being defined, and the way it is defined, reduces unnecessary documentation, unnecessary decision-making, and unnecessary communication between teams.