In the case of turning flexibility at compile time to a fixed set at runtime and the server side only accepts that fixed set, I'd say that's definitely a lot less of a concern than the literal GraphQL queries I've seen in use at runtime by UIs. At that point, your only major concern is how many of those devs use those sans review by person familiar with the storage that could optimize it. After that, your fixed hash request hasn't improved things from a runtime standpoint over a fixed URL request. The disappointing internal team segregation that makes this a required path to go from actual query and programming languages to pseudo ones is concerning.

But for that common approach for APIs you mention, that cost calculator is a bit scary vs limiting the caller. Now if you're a big shop and you need to essentially expose a query language, ok. But for most, the flexibility is really not necessary and bites later with all the possible combinations of requests.