I think that for a studious JW this is a BIG issue to go over. It is no surprise that this is the issue which gave Narkissos doubts. Like he said there is a ton of christology in the bible which totally flies in the face of this JW "ransom sacrifice" concept.
The JWs inherited this "ransom sacrifice", which in actuality was devised by Russell as an integral part of his "Divine Plan of the Ages". In short, it is based upon many of the "divine plan" assumptions which the JWs have since tossed out, leaving the JW version even less warranted than the Russellite version.