That would be a way to do it, but that would require the client to send exact queries. Depending on how queries are constructed, that will not always be the case.
Also, a quick look at the top search query for “Apollo graphql caching” shows that Apollo needs to deconsteuct the object (both for the request and the response) to be able to cache things: https://www.apollographql.com/docs/react/advanced/caching/
(I’m using Apollo here as one of the most advanced GraphQL solutions)
As far as I understand it you can use the request body directly as a caching key. No need to parse it. If you request exactly the same thing there’s no need to re-request it.