The USAF have a requirement for the KC-46A to operate far closer to a threat environment than virtually every other tanker nation. Hence the requirements for systems redundancy, including cable runs etc. are more severe for the KC-46A Pegasus than for the KC-767I or KC-767J.
The KC-46A is also intended to be used as a 'smart tanker', with an associated need for clever comms kit etc., but this isn't a feature of the KC-767I or KC-767J.
A lot of programme delay for the Italian tanker was down to buffet and flutter problems caused by the pods/pylons. Whereas the KC-767J has the 'old-style' boom rather than the latest generation version fitted to KC-46A; the KC-767J is not fitted with wing AAR pods, hence introduction into service with the JASDF was achieved very quickly.