Yep. But API calls traverse the network, and assuming that's via JSON, you're already losing functionality like Date parsing, so the litmus test of JSON.stringi

Yep. But API calls traverse the network, and assuming that's via JSON, you're already losing functionality like Date parsing, so the litmus test of JSON.stringify/parse seems appropriate to determine if you're dealing with a true "data object." If you run into issues with things like Dates, then it's a smell indicating a potential point of divergence in different codepaths that handle the network call differently.