I agree with your point but i know from experience that each denomination thinks they alone have the majority of the revealed truth and that those who are in dispute, though tolerated in Christian love of course, are clearly not listening to the correct spirit. Which doesn't change the fact that their group seemingly has the authority via the Spirit, to interpret. They believe everyone else is wrong or at the very least, not as 'right' as they are.
I know what you mean. When I heard a few Orthodox say "It is the original church. Nothing has been changed," I thought it was just strange, naive immigrant thinking. They all say they are the original church.
But this -- along with the icon of Christ in Majesty -- was eventually to lead to my decision to become Orthodox. (I asked my priest to accept us formally as Catechumens only yesterday.)
It is true -- they all claim to have the closest ties to the Church of Acts.
Yet, who claims:
to have unbroken Apostolic succession
to be the source of the Canon
to teach precisely what Christ taught the Apostles
to have Jesus Christ as its head
a supreme Vicar
worship of the Mother of God
a schism happening every year or so
healing for the spiritual sick
the fullness of the Presence of Christ
unfathomably profound (and utterly applicable) understanding of the Scriptures
liturgical beauty that exists only for worship of our Creator, Savior and Comforter,
artistic works that present the truth of Christ, and the fruits of lives lived in Christ, for all who wish to gain holiness by turning one's own eyes to truth.