Even if you're willing to accept that recruiting rankings are a better indicator of talent than eventual high-major NCAA performance (and I'm not), how much talent is actually there? If you narrow it down to the past ten years and look at HS classes of '09 through '18, there are 16 players on that list for 10 seasons, which does not strike me as an overwhelming number. Of those 16, six did not make it past Groce's first season (two grads, two transfers, one early entry, one Jereme Richmond), leaving only ten players over 8 years. And those are the guys who have been on board for our tourney drought.
I don't think that's an overwhelming amount of talent coming in. I also don't think that a basic count of RSCI top-100 players is really all that valuable. The data is not reliable (i.e. the talent pool varies wildly year-over-year, so not all #78 RSCI guys are created equal). The data is not particularly valid (i.e. there's no particularly strong indicator that the rankings are reflective of talent), especially once you exit the top 30 or so on the list.
The rankings are a tool and one of the best ones we have, but as a dataset they are grossly inadequate for statistical analysis. At the very least, they tell us far less about a player's talent than up to four years of competition against high-major teams will. Unfortunately, that's not very useful unless we're looking at things after the fact. But since that seems to be the exercise here:
Illinois has, for several years, had only a small handful of guys who belong on a first-division B1G roster.
I'm not sure how you can come to any other conclusion after watching six years of this team getting swamped by more athletic and more talented players. And I don't get what the point is, other than to dump on the few good players who are actually coming through the door to play for this team.