If Duke were in the Big East, they would barely have over a .500 record year to year. Lets face it, the ACC is now a 2 team, sometimes a 3 team conference. The old days of the ACC being strong top to bottom is long gone. There is just a whole lot of mediocrity in the ACC now, which leads to glittery Duke W-L records and rankings and high undeserved seedings. High seedings close to home year in and year out means pretty much automatic entry to the Sweet 16. Makes a HUGE difference if you are a 1-2 seed vs a 4-6 seed every year. Duke gets placed in advantageous seedings close to home because CBS wants the RATINGS with the name schools---Duke, NC, Kentucky, Kansas----deep in the tourney.
Duke would have a much worse record every year playing Syracuse, UConn, Marquette, Notre Dame, West Virginia, Louisville, Gtown etc, esp on the road. The Big East beat each other up, and sometimes that hurts BE teams in the NCAA tourney. The BE tourney is easily the most brutal and toughest conf tourney also in the country.