It seems to me, to embrace that position, one must then abandon almost 18 centuries of historical Christianity, admitting there was no visible orthodox church, and all of the visible churches were erroneous (except you take the position of Independent Findamental Baptitsts, in which case 99.9% or so of the world was lost all those centuries, and even now). Evolving or Emergent Protestantism reminds me somewhat of the modern biblical translations. They keep improving. I think this is the Revelation, or perhaps Preterist position, that the Gentiles were left to their own devices after the last apostle passed and the Jews and Gentiles of the first generations were martyred and failed to appoint orthodox successors. This view seems seems incongruent with 17 And Jesus answered and said unto him, Blessed art thou, Simon Barjona: for flesh and blood hath not revealed it unto thee, but my Father which is in heaven. 18 And I say also unto thee, That thou art Peter, and upon this rock I will build my church; and the gates of hell shall not prevail against it. 19 And I will give unto thee the keys of the kingdom of heaven: and whatsoever thou shalt bind on earth shall be bound in heaven: and whatsoever thou shalt loose on earth shall be loosed in heaven.
I think the Moslems argue that the Jews and Gentiles failed and made it necessary for another prophet, albeit not Martin Luther, to arise afterward to lead people out of darkness. I think the Mormons have a view like this, although with different prophets. It seems to me that one ring that binds them all is to try to destroy the Catholic Church. That may seem oddly recognizable if one is not attached to one of the warring parties.
That is exactly what those who put their faith in Christ alone must do. The apostacy and error of "historical Christianity" is evidenced already in Johns day.
That dating depends upon orthodox is defined, as to what degree of error can be tolerated before one is no longer orthodox. One can believer in salvation by grace thru faith yet baptize infants, and may even have some sort of Real Presence view (which term came from the Anglicans), and yet be born again with a poor and contrite heart, thus the salvific gospel is key, without with one cannot be part of the church, that being the body of Christ.
Meanwhile, complete doctrinal unity or purity has never been a constant in the church, while the church that the Lord referred to into which all believers are baptized, (1Co. 12:13) and which is called His body, which He is the head of, (1Cor. 11:3) and which Saul persecuted, but He will preserve, is the one true church as it alone consists of 100% believers, while its visible expressions have never remained without error.
Rome may claim to never have erred, but there is asterisk after that, meaning infallible teaching, which is very limited. Most of what RCs believe and practice has not been defined infallibly, at least according to the opinion of one apologist, thus allowing for possibility of error, if not salvific according to her, and indeed an honest RC must admit that Rome has corrected things that were errors that RC were enjoined to obey (like torture), or else modrrn Rome she has contradicted herself as other RCs say.
Moreover, there are multitudes of things which nothing ever official has been taught by Rome, leaving room for much error.
In addition, what you call Orthodox Christianity either includes the Eastern Orthodox, which means Orthodox means disagreeing about universal papal jurisdiction, papal infallibility, purgatory, and the Immaculate Conception, and more , or it excludes the Orthodox from being Orthodox.
Thus what you mean by Orthodox must be restricted to core teachings, and by the same criteria I can affirm churches which preached (not just professed) the gospel which resulted in manifest regeneration - which we see being the evidence for Scripture-supported Gentile inclusion - as basically Orthodox, while excluding Rome as being so by the time of the Reformation.
Yet as like the remnant which God preserved during the the Babylonian captivity of Israel, the Lord preserved His body as the relative remnant it always was to varying degrees, as Rome was not so deformed that the gospel truths were not available, and so as today, humble and contrite souls could see past the trappings of institutionalized faith and lay hold of Christ to saved them as damned+destitute sinners. And "The Lord is nigh unto them that are of a broken heart; and saveth such as be of a contrite spirit."(Psalms 34:18)
For me, while God always preserved Truth and faith - often by raising up men from without the magisterium to reprove it, and which is how the church began and has continued as the body of Christ - yet the progressive deformation of the church is very manifest, esp. Rome, with the Reformation being necessary but which still must be ongoing to get back to Acts 2-4.
Is your objection that what is promised is a perpetual visible church with one visible infallible infallible head and infallible magisterium that the laity looks to, and which is essential for knowing which men and writings are of God, and to prevent confusion. And thus if this ceased to be a constant reality then that would be contrary to the Lord's promise?