I don't have much experience. I don't understand the complaints around semantic ambiguity. Can't you just declare you aren't trying to build the semantics perfect system, pick one of the options and have things be perfectly all right?
For me it's not about building perfect system. It's this gut feeling that you're using wrong tools. Like you're trying to build a house, but all you have is a set of old car tires and a bunch of duct tape. It just feels ill-suited for the task.
That's not just REST/JSON, of course. That's the general feeling I have from web-ecosystem. Recently I had to work with a simple HTTP form with one field and a single checkbox that is shown conditionally. Hours of debugging revealed that you can't just POST unchecked checkbox [1]. There is no difference between "unchecked checkbox" and "no checkbox". Instead you have to resort to hacks with hidden input field. It's just all feel hackish and you constantly question yourself – am I doing something wrong or it's just this whole stack is a set of hacks on top of hacks?
Same feeling with REST/JSON. Once your API grows past simple CRUD you start caring about optional values and error codes. Ambiguity seems fine until project grows and more people join and introduce inconsistency: one call returns 200 OK for error, other returns 5xx/4xx (cost of choice). Now you have to enforce rules with static checkers and other tools. You bring more tools just to keep the API sane, and it all, again, feels hackish and ill-suited. I don't have this feeling with gRPC - it feels like perfectly designed for APIs.
