This is going to sound like sour grapes but I’m thinking one school might actually waitlisted me for yield protection; they are low-yield (think Drexel) and my LM is about 80. Connected very well with the interviewer who repeatedly praised how great she thought I was.
Actually, it doesn't sound like sour grapes at all. As mentioned above, it sounds like you are tying to rationalize the irrational!
That said, as a mere pre-applicant, I think you are misunderstanding yield protection. Schools receive far more qualified applications than slots to interview them, so most schools other than those at the tippy top engage in some form of yield protection to avoid wasting IIs on people who are statistically highly unlikely to enroll.
Once you have an II, yield protection is no longer on the table, at least not until deciding who to take off the WL, when it will again come into play depending on where else you have WLs or As, how interested you seem, etc. To the extent it happens prior to a decision, it happens on the front end, before the II. Not after a great interview, when they wake up and say "Holy crap! LM 80 -- WL." That's just not how yield protection works.
For what it's worth, there are plenty of applicants with high stats and less than spectacular ECs who turn out to be great fits at so-called low yield schools. Based on my observations of friends who have gone through this last cycle and so far in this one, I really think adcoms know what they are doing, and can tell after a brief glance at an app which high stat applicants are going to be showered with love at T10 and T20, and which ones they actually have a shot at enrolling, and act accordingly. It's not perfect, since every year there are people who get into a single T5, T10, T20 and solicit no interest elsewhere in that group, and they can never figure out why, but, by and large, the adcoms know what they are doing and can figure out who is going to be in play and who isn't.