By your definition, the NT Church died with the last apostle. When the church in Antioch accepted the first council, it didn't cease to be the community that it had previously been as established by the apostles, or when it accepted the second, or the third, or the seventh, or the council concerning Palamism, or the Jerusalem council called in defense of Protestant influence on the Church. Whether you acknowledge it or not, Doesn't change the fact that the community founded by Ss Peter and Paul in Antioch still survives under the current leadership of His Holiness Ignatius IV, as one example.
That doesn't address what I said. Organizational continuity is its own issue, as I'll get to in a minute, but I wasn't addressing that. Rather, I was looking at doctrinal
continuity. And the reality is that it doesn't go all the way back. Ideally we want to meet two standards: that we positively teach what was taught in apostolic times, and that what we teach isn't inconsistent with what was taught in those days. These comprise, in part if not in toto
, the standard of sola scriptura
. Nearly all of Protestantism--and indeed, the deviants such as the JWs are oft excluded because of their heresy on this point--holds that the Nicene Creed can be defended from scripture, though it isn't stated outright. But there came a point at which it had to be formulated, and if you back up into NT times it hadn't been formulated, and indeed the issue had not yet been presented. That doesn't mean that the church(es) at that time believed something at odds with the Creed, but that the Creed had not become a defining characteristic. That is what I meant by saying that it was not (yet) Orthodox.
There has been a great deal of theological and practical elaboration since AD 70. Protestantism arises out of the realization/theory/heresy (take your pick) that late medieval Catholic practice (and the theology behind it) had evolved so as to pick up a number of abuses. OK, well, where to start in criticizing them? Well, at the very least one could say that scripture, not having evolved, could serve as a touchstone. That principle is what lies behind all the various versions of sola scriptura
. After that there is a great deal of disagreement, partly over exactly how it is to be applied as a test, but also because of the various Protestant interpretive traditions. The Eastern churches really don't figure in this except to the degree to which they reflect medieval western practice and theology-- which they do to a very great degree.