Daffodil doesn't pass the datatype for a simple value as part of the StartElement or StartArray events.
This means that you can't, for example, tell whether to create the JSON member as a string or as a number (i.e. whether to include the "" or not).
In XML output, this prevents putting an xsi:type="..." element on the simple types, which is sometimes of value.
Daffodil ships a JSON outputter, but it just renders everything as a string, and the XML outputter doesn't add xsi:type attributes.
The infoset datatype member is required part of the DFDL infoset according to the spec, so the lack of this information is non-conformance to the spec.
The JSON inputters/outputters would have to be adapted to JSON that does not have the "..." around everything.