Indeed. The application contemplated by HTTP is hypertext. If we are being sticklers for the RFCs, modern applications implementing non-hypertext business logic

Indeed. The application contemplated by HTTP is hypertext. If we are being sticklers for the RFCs, modern applications implementing non-hypertext business logic via HTTP are abusing more than just response status codes. But if we relax the “hypertext” presumption a bit and consider HTTP a protocol for the transfer of resources, surely an API can be implemented such that using response codes is sensible and useful. REST and SOAP for CRUD operations can still work just fine, and response codes can still make sense in the context of the API itself, even if the content is JSON describing business logic state. It’s a messy world, so we have to be liberal in what we accept, but using status codes is not inherently abuse. Any ambiguity might just be a symptom of leaky abstractions in the API.