The author states that in their experience, most downstream services are REST, so adding a GQL aggregation layer on top isn't very helpful. It seems possible they would have a different opinion if they were working with multiple services that all implemented GQL schemas.

In that (common) case, the advantage is the frontend/app developers don’t need to know what a hot mess of inconsistent legacy REST endpoints the backend is made of, only the GQL layer does. Which also gives you some breathing room to start fixing said mess.

Being able to federate REST alongside GQL has been a value add in my experience. Apollo even has the ability to do this client side