So, in order to do it in this case, Church Tradition must be rejected. By definition, that is Sola Scriptura.
False doctrine is necessarily an addition to scripture. Apostasy is created by a failure to follow the Bible alone, because "you can't get there from here", so to speak, if you are really following only the Bible. The fact that some *claim* to do so but subsequently adopt a bunch of unscriptural nonsense does not discredit the Biblical approach itself, it just indicts those who falsely invoked it.
Apostasy, by definition, is the abandonment of a previous loyalty. That would include Church Tradition, which includes the Ecumenical Councils. False doctrine is not always a case of addition, but sometimes a case of omission. Or both. In any case, it involves a deviation from what has been traditionally taught.
The idea that someone could read Holy Scripture and, without the guidance of Tradition, interpret it correctly is an attractive idea, but only in theory. In practice, it doesn't work. Different people will interpret it in different ways. Take a look at all the different christian denominations today. Consider, for a moment, what it is that we are divided over. By and large, we are divided over our interpretations. The absence of Tradition greatly aggravates the problem. Schisms become inevitable. Pick up a newspaper and see for yourself.
Indeed. But again, the existence of erroneous interpretations does not preclude or discredit correct interpretation. Unity in doing right would be nice but is not necessary (or even absolutely achievable). Unity in error is worthless.