[gbcdoj]

No father prior to St. Photius that I know of said, "This is but a minor matter", or words to that effect

And what prior Father stated that it was a major matter?

[Graves]

"And what prior Father stated that [unleavened bread] was a major matter?"
Implicitly, I would say St. James the Brother of the Lord appears to have done so, thus the universal practice of the East, excepting Armenia. It would be a part of what the Orthodox call the oral Tradition.