Earlier quoted context omitted.
Pretty sure the author is aware. I think the interesting part is that the frequency is logarithmic and one rotation = 2x. This means you can make musical observations about chord qualities from the plot. That's not generally true for FFT plots.
You are right, it is cool idea in general. But, idk if we are seeing the same thing, in practice it ends up being kinda mushy looking right? In part, I think, because like its not rooted by a given root note, so at best we end up seeing constantly rotating, slightly different clock arrangements. Even in ideal conditions, anything like, e.g., Cmaj7 to Em is going to look almost the same, which feels off given the perc…
Personally, I think it's a feature that Em looks substantially similar to CM7. If this was all working fully as intended, I suppose you might get a clue from the darker-colored bass note.
A bass player probably has a different perspective, but as a keyboard player, it's pretty much always fine to play an Em over a CM7. It's just a "voicing choice".