Just barely better than Kershaw. But he is not the best pitcher, you can't base that off one month of work. Especially when this is the first year in his career his era is below 2.53 and a career 3.90 era. Kershaw has a career era of 2.45.

Plus there is no question that grienke is having a better year than Arietta. 7.8 to 6.1 WAR.