No team in the last 12 seasons has gone onto to win the championship if the first round series lasted more than five games. The last team to do it were the 2014 Spurs who defeated the Mavs in 7 games.
Since then the next list of champions won their first round series in five games or less
2015 Warriors: Won in 4
2016 Cavs: Cavs in 4
2017 Warriors: Warriors in 4
2018 Warriors: Warriors in 5
2019 Raptors: Raptors in 5
2020 Lakers: Lakers in 5
2021 Bucks: Bucks in 4
2022 Warriors: Warriors in 5
2023 Nuggets: Nuggets in 5
2024 Celtics: Celtics in 5
2025 Thunder: Thunder in 4
The only teams that qualify so far are the Spurs and Thunder who won in 5 and 4 games respectively. Lakers and Pistons would join them if they win their series tonight.