The letters to the 7 Churches confirm that Churches had failed seriously in different ways within 50 or so years.
You are aware that those seven churches were not the entirety of the Christian church at the time, but were rather seven specific churches that were having problems; what is noteworthy are the numerous churches which were not addresseed, for example, the Church in Antioch, the Church in Alexandria, the Church in Kerala, the Church in Edessa, the Church in Damascus, the Church in Nineveh, the Church in Jerusalem, the Church in Cyprus, the Church in Rome (actually, the churches of Jerusalem, Cyprus, Antioch, Alexandria and Rome were the autocephalous churches since the first century - all of the churches that were criticized in Revelation were at the time most likely party of the Patriarchate of Antioch, later under the Patriarchate of Constantinople, for they are mostly in Asia Minor).
The Church as a whole, by which I mean the entire collection of churches that are legitimately Christian, that people define in different ways according to ecclesiology (most Anglicans subscribe to either Branch Ecclesiology, Invisible Church Ecclesiology, or the Orthopraxis Ecclesiology of Martin Luther), cannot be in error, but individual local churches can (this is a problem for the Local Church Ecclesiology when taken to an extreme, favored by Baptists and historically by Congregationalists; in my work with the Congregationalists I never adhered to the idea that the Local Church was
the Church for this seemed to be confusing a tree with a forest).
Indeed that is a rather good metaphor - the entire Church is like a forest, which we are promised will never be burnt down (the gates of Hell shall not prevail against it, in Matthew 16:18), but individual local churches like those in Revelations can fall into error, and thus become diseased or perish, or be cut down by schismatics and heretics, as happened to the churches in Boston which were converted to Unitarianism in the 18th century, and thus rejected Christ.