Your argument in favor of the inerrant Protestant canon of Scripture is based on your understanding of history.
This is an extra-biblical argument.
So for your Canon of Scripture to be inerrant, you must be infallible in your argument.
While it is logically possible that your argument is correct, we cannot be certain, since, under your own rubric, no human being is infallible in matters of faith and morals.
2nd Peter 1:21, "For the prophecy came not in old time by the will of man: but holy men of God spake as they were moved by the Holy Ghost."
It's not the man that is infallible, it's that man, moved by the Holy Ghost, became a vassal, which allowed and infallible God to write and say what He desired, not what the fallible man desired. It's something we will never truly understand until we are in His presence.
In addition, Jesus told us His word will never pass away." He used "fallible" man to preserve His "infallible" Word until it could be made into an "infallible" translation that all could read and understand. That fact that an evil organization tried to destroy it, and is still trying to do so, only lends credence to it's infallibility.