I've only had a little experience with GraphQL, but I'm finding it frustrating because designers of the APIs tend to normalize structures since the backend is often a relational (or graph) database.

For example, rather than having top level "admin contact email" and "business contact email", API designers will have a sub graph of contacts, with label->email. (Note that this is the trivial example, it gets much worse)

Most of the time, I need a flattened version to actually do the work. Now, with SQL, that's not an issue because I can put a query together that flattens/joins as needed. But, with a GraphQL result withs lots of edges and nodes, I can't do that simply. I have to write some bespoke recursive walker to pull the data back up.

I understand I could fix this with the schema, but these aren't my APIs, I'm just a consumer. There doesn't seem to be some universally supported way to do the equivalent of a join.

Or, more simply, the culture around REST/JSON seems to prefer flatter structures, but the GraphQL crowd tends to like more nested structures...even when it's not really needed.

Edit: Also, it's not so simple to make a universal, declarative-driven "flattener", as the nested structures vary pretty wildly in how they are done.