My personal study of what ancient writers actually said began in approximately the year 1966, and has filled, not just many years, but many decades. I did not read ABOUT what these people wrote, but their actual words. (Of course, for the most part as translated into English.) A very significant amount of this study has been devoted to what the early Christian writers actually said.
My observation about what we find in these ancient writings is that in the beginning, most of them corresponded fairly closely to what the scriptures actually say. But even as early as the mid second century they were having trouble with people who were supposedly real Christians, (as opposed to heretics) but who were denying basic doctrines.
In the third century, these denials of basic doctrine began to become more "mainstream," until by the sixth century, the writings could scarcely be recognized as having come from the same group.
My personal study of "Patristics," as it is called, has concentrated mainly on their eschatological views. And much of what was written between the mid second and the early third centuries, sounds like it might have been written last week at any one of numerous Dispensational seminaries in the United States. As I have previously documented here:
Dispensational Doctrine before the year 200
And even as late as the fifth century, Jerome called futurism "the traditional interpretation of all the commentators of the Christian Church." (Jerome’s comments on Daniel 7:8, as found in “Jerome’s Commentary on Daniel,” pg. 77, translated by Gleason L. Archer, Jr., published by Baker Book House, Grand Rapids, 1958.)
But it was not only the original views about eschatology that changed. As time progressed, even the doctrine of salvation by grace through faith, was gradually replaced by a doctrine of salvation by good works.
And although there were a few standouts, by the end of the sixth century and for almost a millennium thereafter, there were almost no writers that followed the views of the early Christian writers. (At least, writers whose works have been preserved.)