I have thought about this for all of thirty seconds, but it wouldn't shock me if this was the case. The intuition here is about types, and the ability to introspect them. Agents really love automated guardrails. It makes sense to me that this would work better than RESTish stuff, even with OpenAPI.
Same in terms of time spent. The hypothesis graphql is superior passes the basic sniff test. Assuming graphql does what it says on the tin, which my understanding is it does based on my work with Ent, then the claim it’s better for tool and api use by agents follows from common sense.
This is a task I think is suited for a sub agent that is small in size. It can can take the context beating to query for relevant tools and return only what is necessary to the main agent thread.
