It shouldn't come as a shock that the Brewers outscored the Giants today--the Brewers lineup is generally recognized as one of the more powerful in the game, while the Giants lineup is...not.
The difference is quite dramatic. Nate Roth totaled up the PECOTA-projected VORP numbers for the starting eight, and got a difference of 219.4 to 82.3.
During the game, I looked up the ZiPS projections for the San Fran starters and discovered that, using those numbers and David Pinto's Lineup Analysis tool, the Giants were supposed to score 3.55 runs per game. As I noted in the comment thread, that's 575 runs over a full season, which is almost 100 runs worse than the lowest-scoring NL team last year.
Using the same methodology, the Brewers come out to 4.835 runs per game. (All of this is assuming average pitching.) That's 783 runs per season, which is a bit down from last year. These numbers are all a little low, because they assume the pitcher will bat for himself, and that the manager won't make any advantageous platoon moves. The Giants are probably a little low as well because the ZiPS projections are adjusted for their home park, which is pitcher-friendly. Oh well.
Following Nate's suggestion, we can use those numbers to figure out how today's Giants and Brewers lineups would do in a full season, head-to-head. Using the equation for Pythagorean Won-Loss record, the Brewers would win 103 times over a full season.
That would be nice.