Irrelevant to this discussion? I thought the thread was about whether the acceptance decision is based solely on the interview. It's very relevant to know what is actually happening.
"Shoulda, coulda, woulda." Stating how they should do things is futile consider in it won't make a difference as to how schools will approach the decision. Also, if you you're self haven't had to make these decisions, then it's an uninformed "shoulda." First hand experience trumps.
Lastly, I think so many of us forget that we aren't necessarily competing for spots on a one-to-one basis. It would be counterproductive to pit similar candidate against each other. What you're arguing was somewhat addressed with
LizzyM's staircase analogy. What more is left to discuss?
Edit: also when I read your initial posts, the tone used seemed to indicate that what is wrote is what happens on adcoms.