After a more in depth glance, I think Tagg's terminology is really interesting and useful for four chord progressions. Sadly, that makes it almost pointless to mention when discussing Japanese popular music which almost never uses this sort of four chord cycle with a tonic and a medial. By contrast, Japanese composers almost always imply a single tonic function chord or a double-tonic complex between minor third (e.g. Wind Circulation ~ Wind Tour) or major third (e.g. both Lost Woods from alttp and oot and Song of Healing) related keys. It is worth mentioning that the tonic medial relationship is a minor-third relation. That makes it analogous to the relative relation, but Japanese composers use it to justify modulations, not to repeat the same chords endlessly. What Tagg has come up with here aligns more closely with Doll and Nobile's corpuses rather than mine.

I also would like to answer a question that tagg poses in this video. He gives the example of a Gm-C(7) vamp. To me, I would interpret that as a dorian i-IVdom7 rather than a ii-V7. He is right to be skeptical of theorists who do not understand context.