Something about tourney coaching experience. Of the past 34 National Champions, only 3 were coached by a guy who had never coached past the Sweet 16, and all were in cases where they sort of took over a team, rather than trying to do it with their own team for the first time. You have Steve Fisher in '89 taking over right before the tourney; Tubby Smith basically being handed a championship team by Rick Pitino in '98 when he left for the NBA; and Kevin Ollie taking over for Calhoun for the '14 UConn champs.
I dunno. "Only 3 national championships for coaches that didn't previously make it past the Sweet 16" sounds like the same sort of backwards analysis as "Well this coach doesn't do well because he's not good at beating ranked teams on the road".
I don't know enough to quantify it, but it just sounds wrong.
You know why most coaches haven't made it past the Sweet 16?
Because they're not coaching teams with enough talent to do so. Teams with enough talent to regularly make the EE, FF, and championship game are occasionally going to win it. Teams without enough talent to do so might make a Cinderella run past the Sweet 16, but then they'll hit a team with a LOT more talent in the next three rounds and falter.
I think the only previous Purdue team in Painter's tenure that had a legitimate shot at a National Championship was that Hummel/Johnson/Moore team with Kramer. That team was on fire, and had climbed to #3 in the nation when Hummel tore his ACL. The team without him gritted their way into the Sweet 16, but they weren't the same without Hummel. The next year might have been it again, since Hummer/Johnson/Moore were all seniors, but then Hummel tore his ACL
again during the first practice of the next season. That team likewise made it to the Sweet 16, but they were only 14-4 in conference and ranked #13. That probably should have been an EE team, though, but VCU was on a tear and knocked us out.
Purdue teams have never been ranked in the top 10 come tournament time. The best seed Purdue has ever had under Painter has been a 3, and that was the 2011-12 team.
Expectations are that 1- and 2-seed teams "should" make it past the Sweet 16. Expectations are that teams ranked in the top 8 of the polls "should" make it past the Sweet 16. Every team Purdue has taken to the Sweet 16 has been flawed, which is why they haven't been a 1- or 2-seed and haven't been ranked in the top 10. As a Purdue fan, I sincerely wish Painter had overachieved and taken a 3- or 4-seed to the EE in at least one of those years, but it's not like he had the level of talent as a team where it was expected to happen.
This year is Painter's best team. It's more complete and deeper than even the pre-injury 2010-11 team. This team doesn't appear to be flawed in any particular way I can identify. Will Purdue win it all? Probably not. Only 1 team gets to do that, and a lot of factors [including luck] come into play. But it's unfair to throw out a stat like that without realizing that those sort of stats have context. The context has changed for this Purdue team, because it's a better team than he's ever had.
Your other examples of the three coaches who *had* done it prove my point. Those coaches took over teams that had the talent to be there, so the past experience of their wins wasn't "theirs". So instead of being coaches of strong but not elite teams who rarely had the talent to go beyond, they inherited the talent. How have those coaches done when they didn't have the same level of talent? Probably not as well.