All very valid points. Here's how I'd respond: maybe I'm cynical, but I'm never 100% convinced that an offer necessarily means A) the school is "all-in" on the prospect and/or B) that the prospect is legitimately considering the school. So given our (admittedly abnormally high and probably unsustainable) success rate getting our top targets the past half-decade, the fact that we only hit on two of seven of our top-20 targets seems like an outlier, and that there may be more to the story. We definitely could've "just missed" on some of the top guys. But, perhaps K backed off on some of those guys after the offer upon a closer look. Perhaps he felt the other guys we ended up getting fit at Duke better. One other feasible explanation is that K adjusted his recruiting thinking that there may not be as many "starring roles" available in 2020-2021 based on who the program projects to return.
Again, my main point is that, based on what we know (as far as I know), these are all equally likely scenarios. We'll never know with 100% certainty what the story is with recruiting (probably nor should we, as these are personally decisions made by high-schoolers). But given that this is an outlier I'm not so sure we should dismiss it so simply as "we just missed" on some guys.
To be 100% clear, I am not saying one way or another whether this is a positive or negative development for 2020. Just that it is something that bears thinking about critically, especially as we move forward and see how the 2019 recruits look this year. It's a slightly different scenario than we've been in recently.