You think there weren’t other heretics claiming to be true Christians “from the start”?
Is your claiming it make it so?
I detect some animosity in your comments. Why?
I used the word "we" to include ALL those who claim to follow Jesus Christ as Savior and Lord - but ONLY God sees their heart. Those who sincerely do that recognize the authority of the Word of God, given to us so that we might ALL have an objective and authoritative source to know what is or is not the truth of our faith. The OP talks about early Christian leaders and how they had the Scriptures with which to dispute heresies. Without that, we would only have opinions, ideas, theories and word-of-mouth "traditions" with no sure way to know who is right.
If we didn't have the Constitution to guide our nation, we would not have made it as far as we have and it is the veering away from these founding documents and the intent of the founders that has brought us to this point in our history. Clearly, a group of powerful people, asserting their own way, is not how those who started this American experiment wanted it to be.
God gave us His divinely-revealed word for a reason. We should be servants of it and not make it a servant to us. Doesn't your Catechism say that?