First of all, you seem to be using Tradition to establish Scripture. I am personally fine with that, but I don’t think that is the general Protestant approach. Second of all, some books of the Bible are not so we’ll established. For example Revelation.
Well, that was why I asked you my initial question. What is the canon? The canon is not a manmade construction. As you may know, canon means a measuring stick, it is a standard by which something is judged. The canonical works or scripture are considered canonical because they have their origin from God. In other words, they are the written record of God’s revelation. They are canonical because some books are indeed inspired by God through the Holy Spirit, whereas others aren’t. So from that standpoint, the canon is an objective truth in that some texts are indeed inspired of God, while others aren’t.
That being said, the recognition of what was revealed by God is an epistemological question. How do we recognize what has been handed down from God? In determining that, I have no issue with placing weight on tradition as a tool of providing evidence that gives us a reasonable certainty that what we have is indeed inspired by God. It isn’t infallible, but it does provide some evidence that can be weighed. Look at it as circumstantial evidence being used to build a case in a courtroom.
That being said, you are correct in that some books struggled for canonicity. I have no issue with this. Although Revelation didn’t struggle for quite the reason you think. It was widely held that it was handed down by a trusted source (John), and that it was ancient in its origin (first century). The reason it struggled for canonicity was due largely because there were a number of heresies that attempted to refer to the Book of Revelation, but clearly misused the text. The question of whether it was trusted or whether the content was orthodox was not seriously in doubt, it was more along the lines of being concerned about its misuse. Ultimately, I think the early Church Fathers were right in judging it to be canonical. Getting back to Revelation though, we trust the source, it is ancient in its origin, its content is canonical and in keeping with both Old Testament apocalyptic prophetic revelation as well as New Testament revelation about Christ and the coming eschaton, and ultimately, its prophecies proved true providing additional evidence of its divine origin.