If it is one of the more intelligent, traditional Protestants like a Lutheran, they will usually know an average amount about the early history of the Church and will usually hold no harsh feelings until the Reformation period where they will then state issues they had trouble accepting in the Church. On the other hand, the typical mainline Protestant/American Evangelical really does not honestly know anything about the history. And I know this for a fact because I used to go to school at one of their Private Schools. None of them knew where the Bible came from and many of them, some Pastors included, even thought that the entire Bible existed since the time of the Apostles and believed that the New Testament Church functioned like a Protestant one in the first century, but then when you get to the second century they become clueless and develop all sorts of pseudo-theories and inconsistent claims about the Church becoming corrupted when they do not even know which Church they are talking about. In fact, most refer to it as the Roman Catholic Church because they are either clueless about the schism or do not even know what the Eastern Orthodox Church is.
Sola-Scriptura is fallacious in several ways. The first being the fact that it is unsupported by scripture because you have 2 Thessalonians 2:15, the epilogue of St. John's gospel and that passage in Corinthians (Anyone care to cite it for me?). I've heard some Protestants claim that these traditions were already included into the Bible by the time it was put together, however, that is an inconsistent claim because if they did that, then why didn't they erase those old passages that said to hold onto oral traditions? Or at least leave some indicator saying 'Hey guys, forget about what we said earlier, we already included it in here' or something. Likewise, the New Testament is not a collection of teachings and doctrine; it is made up of epistles directly addressing only certain issues in particular. Then you have the fact that the Bible did not even exist until the middle of the fourth century, arguably sometime around the first or second Ecumenical Council. Which, is rather funny; Protestants believe the Church fell into error yet they still believe they made the right choice in putting the Bible together and developing the Doctrine of the Trinity. So this raises the question of what did the Church do for the first three hundred years before they had the Bible, or the fourteen hundred years before they even had the printing press to make it widespread? They relied on the oral teachings of the Apostles passed down through their Bishops. Moving further, if the Bible was meant to be interpreted individually by each person in the way that Protestants do with no guidance, then why did Jesus say that His will was for us to be one united just like Him and His Father? Because, the Protestants have all interpreted it individually and there are thousands of denominations of them developing each day because they cannot agree on it or have any guidance. Whereas, the Orthodox Church throughout her history has always been able to put heresies to rest and solve doctrinal questions for the most part.
Also, who are the writers/theologians before the Reformation that argued things were going down-hill in regards to all these doctrines creeping in. Basically, I'm asking for a trace back before the Reformation to their side of the argument.
Arius and the Oriental Orthodox theologians, however, most Protestants would not want to be associated with these people and these people rejected the Orthodox Church for different reasons than Protestants.