I will try to answer your questions.
In general, blessed Augustine never challenged either during his life or now. But many saints have a small number of errors in reasoning. St. Augustine may have them, too. I do not know.
For example, it happened that the saint had his own opinion, which he shared with several disciples during his lifetime. But it was of little practical importance. No one used it anywhere. Therefore, there were no complaints. But already after the death of the saint, the devil found heretics who began to spread such erroneous thoughts of the saint en masse, creating a whole new teaching out of them. This teaching led to turmoil in the church. The church was meeting and pondering whether this contradicts the Gospel. If there was a contradiction, then a decision was made to condemn such an opinion or teaching, despite the authority of the saint.
Luther and the Lutherans were never Orthodox. Luther originally belonged to the Roman Catholic (Latin) Church. This church was the first to place the authority of its bishop (the Pope) above the authority of the Ecumenical Councils. In this way, over time, more and more decisions were made that contradicted the decisions of the Seven Ecumenical Councils. This led to the gradual loss of grace and discredit of the church. Protestantism was a reaction to this grief. But Luther, instead of returning to the Orthodox teaching approved by the Seven Ecumenical Councils, came up with a new teaching: everyone can read the Bible and faithfully interpret it as he pleases. As a result, over the centuries, the Bible itself has gradually lost its authority as the word of God among Protestants, because everyone interprets it as it is convenient for them. As a result, we now see LGBT people even among Protestant church ministers. 100 years ago, no one could have imagined such a thing: how it is possible to interpret the Bible in such a way. But by rejecting the decision of the Seven Ecumenical Councils, some denominations distorted the content of the Bible.
As for the symbols of faith, they were also corrected at the Seven Ecumenical Councils, not because something new appeared in the faith, but because the devil and heretics were very inventive. First there was the Arian heresy, which rejected the fact that Jesus Christ is the Son of God and God. That is why the first Creed emphasized this. Then new false teachings, new heresies appeared and the Creed answered other questions.