One thought on your comparison of vocal harmonizers...
In the world of digital electronics, no two events happen at exactly the same time. Korg BATCHES their chord recognition. In other words, there's a slight delay until you get all of the notes down before it recognizes and sounds the chord.

Yamaha, and the MOTL Roland models I've tested all have a bit of a hair trigger. They acknowledge a chord and begin sounding notes as soon as the first key is pressed. Then they use portamento and other effects to bend the notes to the new chord if additional keys are pressed. IMO, Yamaha is the worst offender in this regard. If you aren't super-careful about getting the root down first, it sounds like the bass player swallowed a clam!

If the vocal harmony and/or pitch correction are supposed to be tracking based on the played chord, then Korg will have an inherent advantage, at the price of a very consistent, but slightly less responsive feel to the style player.

Of course I could be tilting at windmills- this may have nothing to do with the widely-held consensus ranking of VH. But personally, I would like to see this "batching" and the window of delay from the time the first key is pressed to the sounding of a chord, as user-adjustable features. I'm aware of the issues with the KN6000 years ago, and I'm not talking about whole beats here. Just something in the range of 25 to 60 milliseconds makes the difference between sounding "arrangerish" and sounding professional. My $.02.