3.7 % of games are against the dodgers, but you're not seeing Kershaw and greinke more than two out of three times in a series, so 2.4% of your schedule may be against those two. It balances and to the extent you get another team's aces, it's too few games to really matter.
Last year, the Nationals got Kershaw and Greinke twice each. The Braves didn't get either of them, at all. Not once.
The whole genesis behind by opposing starter ERA stat that I've kept track of this season is based solely on the concept that it doesn't even out.
...and even if it did even out, that still sucks. I want the Nationals to have the advantage.