Here's an article (not all that well written IMO) that describes the first two years recruiting by the last few coaches. From Lon Kruger to John Groce. Interesting to compare to BU. Kruger and Self didn't seem to do all that well the first year but did well the second. I didn't read Weber (since it was mentioned here already in detail) or Groce.
https://writingillini.com/2017/10/10/illinois-basketball-first-two-years-recruiting-key-success/
It's somewhat misleading in places, because the author considers the first recruiting class to be the class that the coach inherited when coming to campus.
Thus, Weber is credited with McBride, Randle, and Warren Carter for his first class. All three committed to Bill Self, whereas the author suggests that Weber landed them. In reality, Weber's first real class at Illinois was 2004 with Brock and Pruitt. Just the same, Groce's first class was the 2013 class with Nunn, Hill, Morgan, Colbert, and Tate. But the article suggests that Groce's first class was the 0-fer 2012 class.
What Underwood did in getting Mark Smith seems to be the exception rather than the rule. Most new coaches don't add much -- if anybody -- to that very first class they inherit.