We can, with the understanding that no union is possible until it is based on theological unity and not on any agreement on jurisdictional authority of any bishop.
Could the Orthodox come into union with Rome while she reiterated the claims made by Leo and other early pope?
Inasmuch as it is understood that we are dealing with papal opinions and not orders, yes. For +Leo I says "From this formality there arose also a distinction among bishops, and by a great arrangement it was provided that no one should arrogate everything to himself, but in individual provinces there should be individual bishops whose opinion among their brothers should be first"
Even among the most blessed Apostles, though they were alike in honor, there was a certain distinction of power [+Leo I]
I am not sure what he means by "power." If he means ability to do things, I would say, yes because he was given the keys, and only he had possession of them. If it is to mean as being supreme over other bishops, I would say no. Distinction is not supremacy. As the oldest Apostle he received the keys, not because he was better or somehow more faithful than others.
Again, there is no evidence anywhere in the NT that he was given authority to "lord"over other Apostles, not is he ever referred to as the "prince" of the Apostles.
But the Lord desired that the sacrament of this gift should pertain to all the Apostles in such a way that it might be found principally in the most blessed Peter, the highest of all the Apostles [+Leo I].
This is clearly +Leo's personal opinion, not a statement of fact.
"...and that the power of binding and loosing sins was given to [+Peter], who up to this moment and always lives in his successors, and judges..." [Council of Ephesus, 431]
That is rather misleading (if taken out of context), because the power of loosen and bind was given to all the Apostles, not through Peter, but directly by the Lord, although not at the same time, but it was unconditional and independent of +Peter, and that all their successors through them.
That Peter's "supremacy" was not as clear to the Apostles as it is clear to the 21st century Roman Catholic Church is evidenced in the very fact that the Apostles argued who was first among them.
One thing is clear: the office and the power of papal supremacy evolved as is not something the Church taught everywhere and always.
Kosta, your #70 is one of the best summaries of many of the key issues that have been discussed on this thread. Perhaps this is what made it something that no-one wanted to respond to...
1. That the bishop of Rome held a unique Petrine office in addition to being a bishop;
2. That this office was instituted by our Lord Himself and given to Peter alone among the Apostles;
3. That the bishops of Rome were the successors to this office;
4. That this office pertained to the universal Church and not just to the church of Rome.
Again, for the moment I do not want to address whether this opinion was valid, nor what the further attributes of this office are, only that this was the belief of the Western church.