This is from a post a while back on TWEB:
"Apostolic Succession" as typically used by EO and RC apologists here is anachronistic when read back into e.g. Irenaeus or the Scriptures, or other fathers they cite. I will give a thumbnail regarding Irenaeus, the most popular Father used to establish AS as a way to identify the true Apostolic Church.
For Irenaeus, all the apostolic churches taught correct doctrine because they were founded by apostles and faithfully passed down what the Apostles taught--which incidentally was also written down in the Scriptures according to Irenaeus--the true churches could trace their bishops/elders/presbyters back to the Apostles through showing this faithful traditioning from the days of the Apostles down to Irenaeus' day. It was easy to spot the innovations of the various Gnostic sects because their doctrines were contrary to what was preserved by the bishops/elders/presbyters in succession to the Apostles in the Church, and it was equally as easy to show they believed contrary to Scripture. However, Irenaeus apparently assumes that if a Church is in Apostolic Succession, it has the rule of faith, which is similar to the Apostles' Creed and contradicts the Gnostics who also contradict each other. That last is key for Irenaeus, because he often compares the cacophony of the Gnostic doctrines with the homogeneous teachings of the Apostolic Churches.
His system breaks down when one or more bishops/elders/presbyters disagree on what constitutes Apostolic Doctrine and anathematize each other--something which didn't really happen much in his day. It is even worse if groups of bishops/elders/presbyters do this. This causes a breakdown for two reasons. First, if division is evidence against the Gnostics, it is evidence against a group of churches claiming AS. Second, as Irenaeus assumes ipso facto that what the Apostolic Churches teach is the true Apostolic Doctrine, if Apostolic Churches disagree there is now no way to simply say "here is the Church in valid succession to the Apostles because they teach ABC" as could be done in Irenaeus' day. Basically, the schisms of the later Church cause the old wineskins of Irenaeus' AS to burst due to circumstances which did not obtain in his day.
Irenaeus did say that the Scriptures are the same message the Apostles proclaimed, and that they are the ground and pillar of truth.
Against Heresies III 1-2
1. We have learned from none others the plan of our salvation, than from those through whom the Gospel has come down to us, which they did at one time proclaim in public, and, at a later period, by the will of God, handed down to us in the Scriptures, to be the ground and pillar of our faith. For it is unlawful to assert that they preached before they possessed “perfect knowledge,” as some do even venture to say, boasting themselves as improvers of the apostles. For, after our Lord rose from the dead, [the apostles] were invested with power from on high when the Holy Spirit came down [upon them], were filled from all [His gifts], and had perfect knowledge: they departed to the ends of the earth, preaching the glad tidings of the good things [sent] from God to us, and proclaiming the peace of heaven to men, who indeed do all equally and individually possess the Gospel of God. Matthew also issued a written Gospel among the Hebrews in their own dialect, while Peter and Paul were preaching at Rome, and laying the foundations of the Church. After their departure, Mark, the disciple and interpreter of Peter, did also hand down to us in writing what had been preached by Peter. Luke also, the companion of Paul, recorded in a book the Gospel preached by him. Afterwards, John, the disciple of the Lord, who also had leaned upon His breast, did himself publish a Gospel during his residence at Ephesus in Asia.
2. These have all declared to us that there is one God, Creator of heaven and earth, announced by the law and the prophets; and one Christ the Son of God. If any one do not agree to these truths, he despises the companions of the Lord; nay more, he despises Christ Himself the Lord; yea, he despises the Father also, and stands self-condemned, resisting and opposing his own salvation, as is the case with all heretics.
"Tradition" was taught and written down by the Apostles according to Irenaeus. I do not mean by "tradition" here things like praying to the East, but doctrines and dogmas like the Incarnation.
While it is true that St. Irenaeus has a sort of AS which looks like EO AS, it is not really the same. We see that the succession is one of teaching the tradition handed down--and remember that for Irenaeus tradition is written down in the Scriptures and is not another source of revelation. A Christian could have confidence the tradition taught in his church was true because of two factors: The tradition taught is in the Scriptures (Irenaeus has a lot of fun ripping apart the ridiculous interpretations of Scripture offered by the Gnostics, who were the ones who claimed one could not understand the Scriptures without a secret "key") AND that the line of bishops/presbyters/elders could be traced back to the Apostles. This "works" because the Apostolic Churches agree on the tradition. That does not obtain throughout Church history though, because widely acknowledged Apostolic Sees, such as Rome from an EO perspective, lost the "tradition" and so there is no successtion there. Now, since Rome can trace her bishop back to Sts Peter and Paul, she is Apostolic and Rome claims there is a line of teaching back to the Apostles which agrees with her tradition. But it is no longer the case that because a Church is can trace herself back to one or more Apostles that she is therefore Apostolic. Now, maybe there could be councils and majorities of bishops to decide these things--but that is not what St. Irenaeus teaches, that is a later innovation. In other words, reading e.g. EO AS back into Irenaeus is anachronistic.
Irenaeus ipso facto assumes the Apostolic Churches agree in doctrine, hence even barbarians can learn the capital "T" Tradition, just point to the Apostolic Churches and listen. That does not help the EO/RC use of Irenaeus either, because it is not the case that all Apostolic Churches (churches which have been publicly proclaiming the Tradition and who can trace their origins back to the Apostles) have agreed on all points over time--one of Irenaeus' arguments against the Gnostics. So, the current state of the Apostolic Churches means this particular argument by Irenaeus does not really apply today.