Really, I think way too much credit is given to Constantine and the conventions in Rome. After all, they later burned the library at Alexandria and routinely killed, ejected and persecuted everyone who disagreed with their conclusions on a wide array of very dubious doctrinal mutations.
The martyrdom of the saints of the ages, and the suppression of most of the foundational truths of the true Bride and Body of Christ can be traced to the Nicene convention as well.
It was there where a group of bishops who had been in a seesaw struggle for power for over a century, a battle evolved involving intrigue, assassinations and persecutions against each other- a battle only nominally about doctrine. It was primarily about influence with the "christian" Ceasars. According to Josephus, only about one quarter of the bishops invited to the Nicene convention went- and their way was payed, round trip with lodging for anyone who wanted to accept the invite. Maybe those who didn't go knew it was a set up. After all, bishops who refused to sign were threatened with anathema, expulsion from the empire (a dire fate in those days of barbarianism), imprisonment and death.
I believe in the cannon as it is- but I personally believe it was congealing long before the fourth century. The councils were only recognizing a previous historic course. In any case, the histories written by the perpetrators of massive crimes must be read with a bit of reserve. Cain's history would have read differently than Abel's, but then, Abel had no time to write one- he was too busy dying.
It was only because of education, renaissance and revolt against the Roman heel of spiritual, political and ideological dominion that the scriptures were ever translated, printed and distributed to the public.
For me, the scriptures themselves are all the testimony I need that somehow, God, who works all things according to the counsel of His will- did just that, triumphing again over time and man's futility. The burning in my heart is my confirmation.