Async's perfect use case is proxies though- get a request, go through a small decision tree, dispatch the I/O to the kernel. You don't want proxies doing complex logic or computation, the stuff that creates bottlenecks in the cooperative multithreading.
Most API's (rest, graphql or otherwise) are effectively a proxy. Like you say, if you don't have complex logic and you're effectively mapping an HTTP request to a query, then your API code is just juggling incoming and outgoing responses and this evented/cooperative approach is very effective.
