When did the Church fathers write scriptures??
And if ur telling about St.Mark he was the bishop of Alexandria. List of patriarchs of Alexandria - Wikipedia
What u said, i cannot agree because,
While Jesus specifically promised the Holy Spirit would guide the Apostles into all truth, that same Spirit continued to guide the Church after them. The Apostle laid the foundation, but the Holy Spirit didnt abandon the Church once the NT was written.
Jesus said (Jn 14:16-17)
And I will ask the Father, and he will give you another advocate to help you and be with you forever - the Spirit of truth. The world cannot accept him, because it neither sees him nor knows him. But you know him, for he lives with you and will be in you.
So yes, the Church Fathers were part of that ongoing work of the Spirit. They werent inventing new doctrines, but defending and explaining what had been handed down and doing so prayerfully, pastorally and under the guidance of the Spirit.
Anything more if u want to say about this, pls direct it to Does the Bible provide everything needed for Christian faith and practice? not here.