I, and many others, never agreed with any 'altar fellowship' with ELCA. It is contrary to the Anglo-Catholicism of which I am a part. Besides, ELCA is largely apostate. "Valid" is also an interesting term. It can sound quite-snobbish. My view is this-Holy Orders (priests and deacons), ordained (through Bishops that have Apostolic Succ.) by a Bishop, are VALID. Others are 'irregular'. This doesn't mean they aren't clergy, (or aren't churches, for that matter), just 'irregular', not-following the prescribed means of ordination, not in-line with the 'one, holy, Catholic and Apostolic Church'.
You said, "If the office of Bishop is a later development of human invention..." and by doing so, put words in my mouth. Either one believes that the Holy Spirit guided this 'development' or not. I choose to believe so.
Eric also alluded to bishops "... mak(ing) up doctrine and establich new teachings by their own authority," which of course, according to the principles/practice of Catholicity, and the early Church, this was not possible, at least for long.
Of course, these apostate Bishops (like Arius)did do the Church ONE favor--the 'forced' the Church to formulate orthodox doctrines.
Eric also alluded to 'exalted postions'. Of course, there have been Bishops who were anything but servants of the Church. But Bishops should be, as all leaders of the Church, honored and respected.
Again, Eric seems to think that the Bible alone can 'tell us what to think'. The problem, Eric, as I've said a hundred times before, is the question of interpretation of God's inerrant Word.
That is where the magisterium comes in. That is why the notion -read the first page, where I quoted from Vincent and his notion of 'Catholicity' is utterly crucial, and where many Protestants have 'missed the boat'- of Catholicity is important (Wesley understood this, BTW).
Finally, don't confuse 'Catholicity' with being 'Roman Catholic'. The Roman Church certainly did -also- ADD to the Catholic faith (for example, the notion of purgatory and the Immaculate Conception of Mary, and also the notion of her being a 'mediatrix', mandatory celibacy for clergy, indulgences, etc.), and she must also repent of these things IF the Church is to be re-united.