Having three titles doesnt make you the best conference. With the acc it means they have one or two good teams, had the easiest path to the playoff, and got beaten up less than other conferences teams.
That gave them wins, rankings and seedings for the playoff.
Meanwhile BIG 12 teams went through a gauntlet of tough teams in conference, playing a round robin then a rematch for the CCG, plus one or two other P5 teams OOC.
Top to bottom there isnt a tougher conference than the BIG 12 and they have a far better ooc record than the acc.