We parse JSON all the time, there are even ways to generate an JSON-parser-in-Elm for you based on an example!

What we do, is leave this up to generated code. We have OpenAPIv3 specs for our APIs and we use the OpenAPIv3-Elm-client-generator to generate the client so we do not deal with JSON parsing etc. ourselves.

Overhead? You mean in CPU time or development time?

What? I've written a bunch of Elm doing JSON parsing and this just isn't true at all. Writing the decoders isn't hard and gives you nice typed and consistent data formats, which is extremely useful.

I don't know what you mean by "defeats the point of using Elm in the first place", what is the point, and how is it defeated?

If anything, since using Elm I trend towards using things like io-ts or zod to replicate it when I'm working with TypeScript because it is so much better to get that consistency and validation.