it's not only ERA+. They're very close in other stuff

>IP
Pedro 2827
Kersh 2844
>SO
Pedro 3154
Kersh 3039
>K%
Pedro 27.7
Kersh 27.1
>BB%
Pedro 6.7
Kersh 6.3
>Cy Young
Pedro 3
Kersh 3
>ERA titles
Pedro 5
Kersh 5
>Pitching Triple Crown
Pedro 1
Kersh 1