The irony is that you are both agreeing with me and the others in this thread. You say yourself that variations do exist. That's the point of this thread.
Zero people on this thread are complaining about a slightly warmer calibration. And by the way if you think you can tell the difference between 6591k vs 6511k, you are absolutely insane. Those are the measurements of the white point Displaymate got for the X and the XS as posted by 840quadra himself. This is what you are using to "prove" the XS is a warmer calibration. Its absolute nonsense. Those two displays side by side would be visually indistinguishable from each other.
In this thread, we are not seeing XS phones that are indistinguishable from good X phones. We are seeing massive, massive differences. In other words, we are seeing what you exactly call out - there are variations, and they are defects.
As mentioned, there tends to be more defects at launch. To reduce your chances of a defect, buy after 6 weeks. If your iPhone looks distinguishably different than your iPhone X (assuming you got one of the good X screens), you have yourself a defect.