The definition of the CodeSystem property 'type' is clear:

The property value is a code that identifies a concept defined in the code system

we double down on that in the definition of CodeSystem.property.type:

Properties of type "code" contain a code defined by the code system (e.g. a reference to another defined concept).

But then we use code differently. The following standard properties have type code:
status, parent, child, partOf, synonym, and comment.

Comment is clearly an error (see FHIR-44959). Of the others, parent, child and partOf are clearly 'codes that identify a concept defined in the code system', but status is clearly not - at least, we do not - and should not - define the status codes as part of the code system that uses them. Synonym... I'm not sure - see FHIR-44960

Further, in THO we use 'code' for both purposes - an internal reference, and controlled set of values, and we 1200+ uses to disambiguate there

My preference in R6 is to add a property that explains how to interpret 'code' - an internal reference, one of a set of defined codes, or simply conforming the 'code' data type with no extra validation (and then we can pre-adopt it as an extension in earlier versions)