Never

This question was already answered with a careful reading of my quotation of St Vincent.

The answer is never. What difference does it make what the ratio of Orthodox to non-Orthodox? Did it matter that there were 12 Christians, 10 million pagans, 10 million buddhists in 30AD? Did it matter the ratio of those in the church of the apostles compared to the Montanists, Marcionites, Gnostics or Manicheans there were in the 1st century compared to those in the apostolic churches? Of course not.

You want to be able to do what the Marcionites did, which is to set up your own church and decide for yourself which parts of revelation seem to be inspired. No matter if you cut bits out or add bits in, as long as it seems good to you. We say no, the apostles set up a church and passed to it the traditions of the Christian faith. Where else are we to look for truth? You say the scriptures, but what scriptures? The Marcionite scriptures? You can't tell me which ones, all you advise is that the Holy Spirit will tell me which ones. Well, I put my hand up and say that by myself, I don't know which ones. I'm not receiving a 66 book list through the ether. Neither did Luther, neither did Chrysostom. If they didn't, why should I expect it? I'd rather see what the Holy Spirit is telling the Church as a whole.

I must also comment on a possible incorrect understanding. Ecumenical councils aren't as great a consequence as you seem to think. What matters is what the Church believes, council or no council. Councils are just a special opportunity for the people of God to pass judgment on a statement of the faith. Whether 3 or 3000 bishops attend is not the issue, as long as the people of God say "Amen, this is the apostolic faith". This is clearly did not happen for the council of 754.