100% pure assumption on your part. It totally guides all your exegesis to your own detriment. How do you know that ANY of the church fathers got ANYTHING correct? You must assume it.
The text says "when He comes He will guide you into all truth." Unfortunately for us, Jesus was talking to the apostles, not us grunts. He said nothing like "When He comes, He will guide you into all truth, and any disciples that come after you will have inspired commentary so you will know the interpretation of all that I have said to you."
Logic and Christ's promises is why Catholics believe that the Church Fathers "got it right". Who do "you" think is more likely to have been correct---men who learned directly from the Apostles, or a demented monk a millennium and a half later??
"Unfortunately for us, Jesus was talking to the apostles, not us grunts. He said nothing like "When He comes, He will guide you into all truth, and any disciples that come after you will have inspired commentary so you will know the interpretation of all that I have said to you."
Actually, he said precisely that. He promised that "the gates of hell will not prevail" over his Church. The key flaw in the whole Protestant position is their assumption that that Biblical statement was a lie. You assume that "the gates of hell" DID prevail, for a millennium and a half, and then magically, with the advent of Martin Luther, suddenly no longer prevailed. Sorry, but that notion is simply neither logical nor supported by Scripture.