I have posted charts plotting Royals seasons by team ERA+ and OPS+ in the past, charts that were inspired by posts on Bay City Ball and The Hardball Times. The Hardball Times piece by Paapfly was especially interesting to me. It seemed to show that pitching was an absolute must to win a championship, but many sub-par offensive teams have managed to win it all. This seemed to prove the adage that pitching is indeed what wins championships. Here is my version of Paapfly's chart plotting champions by their team ERA+ and OPS+:
I recently found myself reading through the comments on Paapfly's post, and then on a thread about the article on Tangotiger's The Book Blog. Commenters pointed out several flaws with using OPS+ and ERA+ as the measure of a team's offense and defense. Paapfly himself took those suggestions to heart and wrote a second piece in which he made some adjustments but still used ERA+ and OPS+.
Several commenters mentioned runs scored and runs allowed would be the way to measure. And of course, nothing gets closer to the heart of offense and defense than runs. As far as I know, no one took the suggestion and plotted the World Series winners by runs scored and allowed. I have done that below, comparing each championship team's RS/G and RA/G to their respective league's seasonal average. There is no park adjustment, something that would probably improve the accuracy a bit, but the raw numbers were good enough for me. It does tell a different story than OPS+ and ERA+:
The average champion has scored .5 runs per game above average, and allowed .6 fewer runs per game, perhaps suggesting a slight edge to teams who excel at run prevention more than run scoring. But the vast majority of the time, it is both pitching and hitting that win championships.
..."Pitching wins championships." I don't think that's quite right. I think there are more great offensive teams that have won the World Series than great pitching teams. It's just that most of the great offensive teams also had at least good pitching. The 1992 Toronto Blue Jays heavily leaned offense -- they finished ninth in ERA. But that's pretty unusual.
On the other hand, several of the best pitching teams to win the World Series -- and the 2010 Giants fit right in -- had subpar offenses (at least until the playoffs). So I don't know that it's right to say that pitching wins championships. But I do think it's fair to say that you have a better chance to win a championship with great pitching and terrible hitting than the other way around.