The big canon violation is already so obvious that there's no point in even questioning what it is.
Decades before Kirk commands the Enterprise, they see what Romulans look like. Totally "erasing" Balance of Terror.
That's what I keep coming back to. Nero brings the Romulans back into the Trek world years before BoT.
As heresies go, that seems a far bigger one than splitting hairs over whether or not Kirk was born in Iowa or simply lived there. Especially since there's nothing on screen about where Kirk was born or the fate of his parents.
On the other hand BoT is
on screen proof of the first contact with Romulans since the war the led to the Federation (or to put a finer point on it, at least Kirk's first contact). Orci and the others are saying that this movie
starts the conflict with what fans will recognize as a major violation of canon. It flies in the face of one of the most popular TOS episodes.