One final point: "fateantur" is in the subjunctive. It clearly means "
if they deny being committed to Peter and his successors,
then they would be confessing themselves not to be sheep of Christ"--so only those Greeks or others (Protestants) who deny in any way that Christ committed the Church to Peter and his successors, would be denying they are sheep of Christ and would be damned. Anyone who accepts Mt. 16 and Jn 21 as in principle committing the Church to Peter and his successors but who disputes the exact nature (jurisdiction) arising from that general committing would thereby acknowledge being one of the sheep of Christ and can be saved.
Some Protestants acknowledge that Mt. 16 and Jn 21 teach a Petrine primacy; many even recognize that Mt. 16's reference to Isaiah means that Peter's successors are included. Others give a blanket denial. So some Protestants come within the excluded category in this line from Unam Sanctam but other Protestants do not fall into that excluded category. The same would apply to Orthodox, depending on whether they reject absolutely any Petrine primacy or any primacy of honor to his sucessors.
Wow. Eye-opening, brother. You are indeed a treasure - as are so many converts. God Bless you for taking time out of your busy schedule to address this. I think it might soothe a lot of turmoil this Document has given rise to.
Bishop Sheen said "There aren't even one hundred people that hate the Catholic church, but there are thousands who hate what they mistakenly believe the Catholic Church to be."
God Bless you for putting this contentious Document into context and explaining it.