I watched the full game replay very recently and watched it live at the time.
They were 11 AdjEM better over the season than us. That's the difference between this year's UConn and Villanova. It isn't a small gap. UConn were 9.5 point underdogs in Vegas. And if they played again, even after UConn won, I know that Duke would still be favored considerably by the bookmakers. It's dumb to use one game's worth of observations to make a grand claim about a team's ability, and there are people arguing that not only was UConn better in that game (which I agree with), but further that Duke was overrated in general... when they're literally the best rated team of the last 20 years with huge margin ahead of the pack. They won 33 games by double digits that year! Many champions don't even win 33 games total (like both 2011 and 2014 UConn teams).
As to UConn being more battle-tested and more mentally tough... Duke went exactly as far as UConn did the previous season, but lost to the eventual champion by 2 points and missed a late deep 3 at the buzzer. They returned 5 of their top 6. Duke played 7 top 10 AP teams that year before the title game and beat all 7 with an average victory margin of over 10 points, and 5 of the 7 were on the road or neutral court. UConn played 4 top 10 games total, so Duke won more of them on neutral/road than UConn played total. It's great to come up with post hoc narratives because of how the one game played out, but it doesn't make them true. Duke was less mentally tough because Langdon's floater in the lane with 1 minute left rimmed out and then he traveled, but UConn is mentally tough despite El Amin airballing a floater with 30 seconds left and the team up 1? Unless the argument is that Duke was so good that they were inexperienced in close games, but I don't recommend making arguments that a team is overrated because they're too good.
Avery, Battier, and Maggette (three future top 15 first round picks) went 8/26 and UConn's bench went 7/9 from 2. Did UConn play great defense? Abso-freaking-lutely we did. But those Duke guys literally shot over 60% from 2 on the season combined and got plenty of open shots due to the aggressive doubling of Brand. They just didn't make them in this 1 game sample