I believe that you are correct. I believe the issue at hand is whether or not Trump defamed Carroll by calling her a liar.
If Trump did in fact rape Carroll, then Carroll’s accusation is true. That would make Trump’s act of calling Carroll a lair into an act of defamation.
If Trump did NOT in fact rape Carroll, then Carroll’s accusation is False. That would make Trump’s act of calling Carroll a liar into a simple statement of truth and not defamation at all. Also, it would make Carroll’s act of claiming that Trump raped her into an act of defamation.
While this is formally a defamation case, the question to be answered is: “Did Trump rape Carroll?” Who defamed whom all hinges upon that.
Only Trump and Carroll know the truth of the matter. I’m totally convinced that Trump is innocent and Carroll is lying, but if the judge gets the jury to vote in Carroll’s favor, the media will treat it as proof that Trump is a rapist.