I have done the research. The last champion to have real contributions from one and dones was Duke in 2015. Baylor, Virginia, Villanova, and that UNC team were all multi-year players. The 2017 UNC starters were 3 juniors and 2 seniors. Tony Bradley was a freshman and came off the bench.
Then, in 2013 and 2014, UL and UConn did not have one and done contributors. 2012 UK obviously had significant contribution from one and done players. The 2010 Duke team was all veteran players.
So, there are two seasons out of the last 11/12 that had serious contributions from one and done players, and even those teams had veteran leadership at the guard position.