> On the flip side, I've never been frustrated by getting too many fields back from an API

A pretty common use-case I have is needing to support these three things :

- A “big object” list screen (where retrieving the whole objects would make the query return megabytes off data)

- A “big object” details screen (where I need the full object)

- Programmatically getting many big objects

With GraphQL it involves writing one (or two) straightforward queries, while with REST it would require more thought or code.