Davie basically brought in the equivalent of enough 4-star talent to keep us in the top 25, even if he pissed away many excellent offensive talents (David Givens, Javin Hunter, Tony Fisher, the list goes on and on).
Willingham had one good year (2003), where he was able to ride the high of being named Coach of the Year for that freakishly lucky 2002 season, and was able to passively put together a good class. His same approach of "recruit by osmosis" in 2004 and 2005 generated the two worst classes of all time.
Weis brought in more 4 and 5 star talent than we had ever seen, but even these recruits weren't ready in time to offset the terrible 2004 and 2005 classes. His biggest flaw wasn't recruiting; it was trusting the wrong person to run the defense that caused every loss in 2009, thanks to that idiot Jon Tenuta. In retrospect, he should have kept Rick Minter until a truly excellent DC were available and willing to come. That alone would have flipped 2-3 losses in 2008, and at least 4 of those losses in 2009 (conceivably even all of them).