With the current move to using swh.model objects as much as possible, we no longer need to also pass the object type as argument. See eg. the JournalWriter.write_additions() for example:
def write_additions(self, obj_type, values) -> None:
in which values is expected to be an iterable of model objects of object_type type.
In order to prevent the usage of is_instance everywhere, a simple solution is to add an attribute to swh.model.model classes (typically `.object_type') as Final attributes.
This idea has been proposed in D3152, however, the current implementation is stuck because of the way lazy-loading capable Content are implemented (subclassing the Content model class).