There has to be some kind of direct connection between the communications systems and the flight critical systems for any of that to even be remotely plausible. That kind of connection is basically impossible to hide, and simply would not exist in a well designed piece of military hardware. It's existence would be immediately obvious to the people buying the plane, and the people tasked with maintaining it.

Show me one single military analyst with worthwhile credentials who believes this is a serious concern. Not articles like this one where they take a quote wildly out of context and use it to backup an entirely fabricated claim. I mean an actual certifiable expert stating clearly and unambiguously that the possible existence of this killswitch is something we have to be worried about.