Pero James no le has puesto campeon. Diminutivos de James en ingles:
English:
Jacob
Jakob (uncommon, by way of German, Yiddish, etc.)
Jacoby (rare, chiefly American, and originally a surname)
Jake, Jakey (diminutive)
Jack, Jacky, Jackie (diminutive, chiefly British)
Coby/Koby (diminutive, uncommon, chiefly American)
Jamie (diminutive, found in all primarily English-speaking lands, United Kingdom, Ireland, Canada, United States, etc.)
Jaime/Jaimie (diminutive, uncommon, chiefly American, and by way of Spanish)
Jim
Jimmy/Jimmi/Jimi (diminutive)
Jimbo (diminutive)
Jambo
Jay
Jamesy
Jem (diminutive, also taken as a diminutive for Jeremiah, Jeremy or Jemma)
Jacqueline/Jaqueline (feminized, by way of French)
Jacqui/Jaqui (feminized diminutive), Jackie (feminized diminutive, chiefly American), Jacki (feminized diminutive)
Jamie/Jamey/Jami (feminized).
https://en.wikipedia.org/wiki/James_(name)Y tienes razon con John. El diminutivo de Jonathan es Jon.
Un saludo