Since the season is about one-third over (teams have played 54 games or close to that number), it might be a good time to look at this.
I've done some research before where I came up with the following equation to explain a team's winning percentage
PCT = 1.21*OPSDIFF + .5
Where OPSDIFF is OPS differential, a team's hitting OPS minus the OPS it's pitchers allow. OPS is on-base percentage plus slugging percentage. You can read that earlier study here.
In the graphs below, teams in each league are ranked by OPS differential. The next column shows each team's actual winning percentage followed by their pct predicted by the equation. Then their actual wins, predicted wins and the difference.
The Angels have a -.030 OPPSDIFF but have a .571 winning pct. Maybe they have been lucky so far this year. But check out the Astros. They have a -.060 differential yet have a winning record! Then there are the Twins who have a winning record with a -.069 OPPSDIFF. So far, the Cubs and Red Sox are the strongest teams in their respective leagues. The Braves are very strong, too, but their record so far does not show it.