Have you ever debated with a Greek Orthodox and how did you handle the conversation when they brought up their traditions being able to trace back to the early apostles? They seem to think we ignore history for convenience's sake. They also say we are a group that started in the 1800s so how can the church be lost for that long till the “churches of Christ” came into the fold in America?
My first question would be to ask why the Greek Orthodox traditions are different from the equally old Roman Catholic traditions. "Old" doesn't necessarily mean accurate.
"I am amazed that you are so quickly deserting Him who called you by the grace of Christ, for a different gospel; which is really not another; only there are some who are disturbing you and want to distort the gospel of Christ. But even if we, or an angel from heaven, should preach to you a gospel contrary to what we have preached to you, he is to be accursed! As we have said before, so I say again now, if any man is preaching to you a gospel contrary to what you received, he is to be accursed! For am I now seeking the favor of men, or of God? Or am I striving to please men? If I were still trying to please men, I would not be a bond-servant of Christ. For I would have you know, brethren, that the gospel which was preached by me is not according to man. For I neither received it from man, nor was I taught it, but I received it through a revelation of Jesus Christ" (Galatians 1:6-12).
Even at the beginning of the church, people were straying from the truth. If those deviations continued to this day, they would be no more accurate than they were when they were first introduced.
Is the person you are talking with claiming that the traditions they uphold are inspired by God? If so, why are there conflicts between traditions? Why are there conflicts between traditions and what the Bible actually states? As Samuel pointed out, "the Strength of Israel will not lie nor relent. For He is not a man, that He should relent" (I Samuel 15:29).
In regards that the churches of Christ started in the 1800s, see: