1: What happens if you use a different VSTi instrument for the C minor chord (the triad). Is it exactly the same?
Every VSTI is different. Most modern VSTIs, however, use the root sound. If it's a triad it's going to be messy.
I viewed the video and listened to the sample.
2: What happens if you use a completely different VSTi?
This question is no different from the first one.
I viewed the video and listened to the sample.
3: Is the VSTi attempting to arpeggiate the chord?
Chords often mess up the Vsti sound.
PS: You mentioned "From this design, the BIAB is missing a problem."
That would actually be a good thing, yes?
Missing a problem is not a good thing. Chords can cause some Vstis to be unusable. The noise is too loud.
Of course, I can change it myself. But that would be a waste of time, so I came up with this suggestion, which is to add a feature that plays only the G notes of the G chord and only the E notes of the G/E chord on the chord track.