There is virtually no difference there.....especially considering Arriet a piches in a hitter's park and Greinke pitcher in a pitcher's park. Check their road ERAs for apples to apples comparison.
Arrieta has more wins, lower batting average against, more strikeouts, more complete games, more shutouts. Plus, Arrieta has finished the season off stronger in historic fashion in a type of 3 or 4 month run of domination never before seen in baseball......at least not since the end of the deadball era.
It's over.