Certainly the various misrepresentations of teachings needs to be dealt with. However, from my own experience, while Fr. Romanides might have been one of only a few EO authorities who offered a critical analysis of EO history, the vast majority of EO clergy I have come into contact with have been quite open to the idea that Dioscoros and Severus were essentially Cyrilline, and therefore Orthodox. Reading the works of people like McGuckin and Mayendorff, the OO are generally criticised for not being open to Chalcedonian language, not for any actual heresy. Thus, to a large extent, I think a lot of ground has been made on this issue.
What you say about the nature of an Ecumenical Council seems like the more difficult issue. The anathemas of the OO churches were made on a local basis, and can therefore be overturned on a local basis. But those of the EO church were made by an Ecumenical Council, which puts the EO in quite a difficult position. Also, for the EO to unite with the OO without their acceptance of Chalcedon would mean accepting that, however valid its defence of orthodoxy, it was not an Ecumenical Council. That is the implication of such a union. And if the OO have indeed been part of the Church of Christ all along, how could the 3 subsequent Synods be deemed Ecumenical?
So one would have to ask, what makes a council Ecumenical? You mention that Chalcedon was rejected by half the Church, but wasn't Nicea followed by a period in which the Church was dominated by Arians and the orthodox party were in the minorty?
Is an Ecumenical Council infallible?
Is the acceptance of an Ecumenical Council necessary for being part of the Church? If, for example, the Assyrian Church of the East clearly and unambiguously affirmed an orthodox christology, repudiating anything perceivably Nestorian, but refused to accept the Council of Ephesus, could they be admitted into communion with the Church?