Looking at the World Series Champs beginning in 2000:
19 Championships
The AL won 10, the NL won 9.
The team with the best record from the regular season won 5 times, or 26.3%. (2007 Sox, 2009 Yanks, 2013 Sox, 2016 Cubs, 2018 Sox)
The team with the worst record from the regular season won 4 times, or 21.1%. (2000 Yanks, 2006 Cards, 2011 Cards, 2014 Giants)