This one I definitely disagree with (I'm the one who upgraded the northbound lanes to tertiary). The reason for this has to do with the one-way configuration of 600 S and 500 S in this area.

All westbound traffic on 600 S is forced to make a northbound turn onto 600 E. Due to the configuration of roads in the area this is not an uncommon movement to make. Thus, the northbound section of 600 E here serves more than just local traffic: it serves a decent portion of the traffic that wants to access either westbound 400 S or 500 S.

In contrast, the southbound section of 600 E in this area serves no such purpose: it's the definition of an unclassified road that serves no purpose beyond local access to the businesses along it (or a bike route, but that's irrelevant to road class). This is borne out in my experience driving and biking in this area: the northbound lane has easily at least twice the traffic of the southbound lane.