There is no magical limiting factor or quirk preventing a team from winning the championship.
Take the 2014 team, for example. As an 8 seed, they played passable defense in two games, one of which was in the championship, and won the rest through brute offensive force. They won 3 games despite their opponent scoring 1.2 ppp or more.
The "championship teams need x quality to win" tends to also correlate with just being an elite team. Most elite teams are very good on offense and defense. That's why they are elite.