Here is an article that says since 1969 - when playoffs started - only 12 teams with the best record have gone on to win the World Series.
Since the article - which is from 2018, you can add the Red Sox in 2018 and the Dodgers in 2020.
In 2019, the Nationals, a wildcard team with a record of 93-69, won the World Series.
In 2021, the Atlanta Braves, who would have finished 19 games behind the Giants, won the World Series.
How many teams with season's best record won the World Series? - Sports Illustrated