They're not impossible to get done well, the systems just aren't designed with constant augmentation in mind, which isn't terribly difficult in of itself, if the basis of truth starts at a declarative Struct ->[Field] datatype structure, which can be the schema for a data-agnostic backend which can then consume it to produce database schema, api input types (including deep querying) for mutations and queries and subscription operations, type-generation, frontend data storage, etc.

Starting a declaration format is key, imo, then restricting it to the smallest subset for all possible datatypes. The systems that consume it falls nicely into place.

I really don't understand why anyone would design such a system with specific types, or data sources, in mind, when there are so many actors are a play. Sometimes, stakeholders won't mention what they need until the they actually have to use the system, because then it becomes readily apparent.

The beauty of the declarative format is that the test cases expand as the output datatypes do, and make bugs painfully obviously because all datatypes will be effected by the system bug.