The whole point of the wide staircase is that you can go to the top step, or one down from the top, etc at any time in the interview cycle. Even schools that accept some applicants early and others later in the season can put you on the top step regardless of when you interview. I would wager that many schools interview enough applicants to fill the class in the first month of interviews... the rest are not interviewing for the waitlist. Everyone is being ranked throughout the cycle and the top applicants are being made offers throughout the cycle. That doesn't mean you won't be waitlisted, or left in silence for months and later waitlisted or rejected but I can't imagine a school that isn't continuing to interview hoping to snatch up some late-cycle stars.
So, I want to ask this question in a way that you are actually at liberty to answer.
Assuming a ranked WL school that generally interviews its most promising,
meritorious candidates first... and that, as you claim, could easily fill the class in the first month of interviews... we can assume few of them will be outright rejected and the resulting waitlist of candidates will be similarly composed of a high-density of applicants the school believed would score highly post-II.
It is hard for me to imagine that, with the harsh culling of applicants through the interview process, that very many would populate the lower steps of the staircase (if they were just
weird on the interview, they would've gotten an R). I am imagining less of the wide staircase of a grand ballroom, and more a step stool in which most applicants are elbowing one another to get onto the top step and the discernment between individual applicants is much harder because
everyone is practically at the threshold. It would seem like the distinctions between admitted applicants and those on the top step are similarly vague...
We could normalize those scores again so that we have more obvious distinctions between applicants, but the more you do this, the more you are in some ways splitting hairs and/or using math to abstract differences that are so small, they no longer correlate with any meaningful metric.
For someone like me with less competitive metrics, I foresee two big problems with interviewing late. The first is what I mentioned earlier, there are just more people on the staircase. But the second is still a selection pressure: if your initial WL is composed of people the admissions team has already vouched as high-value by any qualitative standard set by the committee, the probability of "less promising" diamonds-in-the-rough not only outperforming the earlier admitted candidates, but also a set of benched wunderkinds seems increasingly unlikely (and laughable as a strategy).
I understand, in theory, that schools don't interview for the waitlist, but I feel I'm missing a crucial piece of information to make that make sense. I know, intuitively, that there must not be "no chance," but I do think the slope can rise enough such that the "uphill climb" is essentially equivalent to "no chance."