I think it depends on the application. In many cases, encoding/json is fast enough and stable, but I think you can try to use a faster library if JSON encoding / decoding is performance critical on your application.

Or you could try something like Apache Arrow or Flexbuffers?

If you write off the "JSON", sure, there's a bajillion options. But that's not always possible or desirable. None of those bajillion options have the combination of support and mindshare that JSON has obtained, for better or worse.

We're talking differences of a thousandth of a millisecond (0.001ms) for most structs, but yes.

encoding/json from stdlib makes a lot of allocations (~30) due its use of reflection, which is notoriously slow.