Here is how I see our disagreement about yechi.
Suppose we would C”V see a minyan insert yechi or something similar into the middle of kedusha or kaddish. You would think that they are putting yechi on a celestial level. And I would think that they just do not know the concepts of kedusha.
As I’m typing this, I realize that this could be a fundamental difference in how we view this whole topic. [As well as some others.] Your thinking is that yechi is an addition. Like a new concept. And I see it as they are missing something and use yechi to fill the void.