A response to the accusation that the Reformer's gospel was newfangled doctrine, due to failure to abide by church tradition.
Our goal is indeed to believe what the apostles believed, and---lo and behold!--they left us some writings of their very own, their very own thoughts recorded on pages intended for us to read. If we desire to believe what the apostles believed, then our sources are the apostolic writings themselves (obviously), not a handful of contemporaries who can at best provide us with second-hand information that may or may not be accurate. Ad fontes. In the Scriptures is where the minds of the apostles are found. The Scriptures are given to us for our learning (therefore they are sufficiently perspicuous), and whatever does not agree with the Scriptures is error. This is the common sense wisdom of Sola Scriptura.
This is especially important to grasp in light of the fact (a fact you admitted) that many contemporaries of the apostles were heretics and/or greatly confused. Proximity is no guarantee of truthfulness. The New Testament itself attests to that.
Martin Luther was faithful to the tradition of the Catholic church, by which faithfulness he never obtained peace nor the true knowledge of Christ and God. It was only when he studied the Scriptures for himself and allowed them to speak to him that he was enlightened and set free.
If you examine the heart of Protestant theology and compare it to the Bible, you will see that what Protestants hold dearest is no 16th century novelty but the very heart of the Christian Gospel as found in the Scriptures: salvation by grace through faith alone in Jesus Christ. This doctrine is plainly taught in the Bible. "But now the righteousness of God apart from the law is manifested... the righteousness of God which is by faith in Jesus Christ unto all and upon all who believe." (Romans 3:21-22). "For by grace are you saved through faith, and that not of yourselves, it is the gift of God. Not of works, lest any man should boast." (Ephesians 2:8-9). "Knowing that a man is not justified by the deeds of the law, but through faith in Jesus Christ." (Galatians 2:16). There are too many to cite in this comment. There is no anachronism. Your charge is unjustified and unjustifiable. But if you want to prove your charge of anachronism true, you must (interestingly) end up doing biblical exegesis, the very thing Protestants insists we do, and have been tenaciously doing for the last 500 years.
To me, the irony of the accusation of anachronism against Protestants is that those who aggrandize church tradition and then proceed to read that tradition back into Scripture are the ones who are guilty of anachronism. Anachronism doesn't take much time to happen, and fidelity to Scripture can happen after a long time has passed. I can personally see nothing but anachronism in how non-evangelicals handle the Bible (ex. Chrysostom says, therefore the Bible says). Evangelicals don't say "Luther or Calvin says, therefore the Bible says", but rather, "Luther or Calvin says, therefore let's go to the Bible to see if this is true." Which method best safeguards us against anachronism? I believe a child can answer this question.
May God make this plain to you,