I think there's some recency bias on the value of "one and dones" based on what Duke and Kentucky have done the last few seasons. Since 2000, more often than not, the eventual national champs are led by veterans:
2015 Duke: led by one and dones.
2014 UCONN: veteran backcourt led by senior Napier and junior Boatright.
2013 Louisville: all around veteran team.
2012 Kentucky: one and dones.
2011 UCONN: Kemba Walker was a junior.
2010 Duke: Very veteran team led by juniors Singler and Nolan Smith.
2009 UNC: Led by senior Hansbrough and juniors Ellington and Lawson.
2008 Kansas: Chalmers and Rush were juniors, Arthur was a sophomore.
2007 Florida: Noah, Horford, Green, Brewer were all juniors.
2006 Florida: Same guys were all sophomores.
2005 UNC: Felton, May, McCants all juniors with a major assist from one and done Marvin Williams.
2004 UCONN: Okafor and Gordon both juniors
2003 Syracuse: Carmelo was a one and done.
2002 Maryland: Dixon and Baxter were seniors, Blake and Wilcox were juniors.
2001 Duke: Battier was a senior, and J Will, Boozer and Dunlevy were all sophomores.
2000 MSU: Cleaves and Peterson were seniors complimented by super freshman Richardson.
That's not to say there weren't major contributions by freshmen in several of those years, but as a rule, to win the national title, you need your stars to be veteran players.