I agree that the Henotikon is another indication of the general agreement between the two parties even at an earlier stage in the controversy when 'two families' had not formed at all.
St Severus accepted the Henotikon as a theological document. His issue with it was that it left Chalcedon unresolved.
I have never read the Second Agreed Statement as requiring that our Orthodox communion decide that our criticism of Chalcedon was a mistake. As I have stated, the SAS speaks of two families of Churches, and these did not exist until post 565 AD-ish. By this time, even when the Orthodox leadership was under immense pressure to be united with the Imperial Church they were unable to do so because of the issue of Chalcedon, yet even at this point they did not seem to want to make up false allegations about the Imperial Church. They did not produce a list of other issues which caused them to be separated. It was Chalcedon which was the issue.
It seems to me to be possible to hold an Orthodox Christology AND also accept Chalcedon. This is what the SAS says. But this does not require that we say that Chalcedon is ecumenical, nor that we say that anyone who accepts Chalcedon is Orthodox. It is also possible to hold an heterodox Christology and accept Chalcedon. It depends entirely on what a person means by 'accept Chalcedon', and this seems to have also changed over time.
There is a real sense in which Chalcedon became simply a polemical standard in the later controversial period. The Chalcedonians were unable to stop saying 'accept Chalcedon', and the Orthodox were unable to stop saying 'reject Chalcedon', for understandable reasons on both sides. But Chalcedon had already been accepted, rejected, accepted, rejected and finally accepted by lots of Imperial bishops, often the same bishops. This is because they held neither a strictly pro-Chalcedonian nor strictly anti-Chalcedonian point of view. They may have been at fault in this regard, but I am not investigating that issue, rather it seems to me to show that there were many bishops who for a variety of reasons were able to change their view of Chalcedon without it would seem to me changing their Christology.
It would therefore, it seems to me, be wrong to consider all those who accepted Chalcedon as having the Christology of Ibas and Thedoret, even if I do consider that one of the weaknesses of Chalcedon is that it made room for such views, and I am not convinced that Constantinople 553 eliminated them. But this is to judge Chalcedon - which I am more than willing to do in another context - it does not absolutely judge all those who accepted Chalcedon.
How did they accept Chalcedon? Especially by 565 AD? I would suggest that it was not in the same way that Theodoret accepted Chalcedon - writing to his supporters that his Christology had been vindicated. It was not in the same way that the large numbers of Chalcedonians who accepted the Three Chapters viewed Chalcedon. So it seems wrong to me to insist on only one way of 'accepting Chalcedon', just as I have insisted over 16 years online that there is more than one way of 'rejecting Chalcedon'.
When I read John of Damascus it seems to me that there are not very many differences between the Church he is a member of and the Orthodox Church I am a member of. Yet he does show his ignorance of our tradition in some places. Is this enough to say that he has not preserved the same substance of faith? I am hesitant to say so. It seems to me that he almost describes a unity of faith but withdraws from doing so. I find him frustrating in that regard but I don't find him promoting the Christology of Ibas, Theodoret or Theodore. When I read his passage on the two natures it is annoying because he obviously is not understanding the Orthodox terminology and is therefore writing against a straw man, but in terms of what he actually says, and reading it with his understanding, his own Christology does not strike me as being one that I could say was not Orthodox. Or perhaps was Orthodox enough.
His initial description of the will in Christ, for instance, is very close to what I would say, and is certainly far from those EO I have corresponded with who have taught that Christ has two different and contrary wills. I do not entirely accept his view but I cannot say that it is the same as the view which would divide Christ.
If I were in discussion with John of Damascus I hope that we would find much to agree with and we would say of each other that we had found the same substance of faith. Then we would have to deal with issues such as the status of Chalcedon. But it is almost fanatical to begin with Chalcedon, on both sides, since that precludes any discovery of agreement. Our hierarchs have engaged in such discussion and have found that which many of us also have understood, that there is a substantial unity of faith between the EO and OO. This does not remove obstacles to unity, but it does mean that we begin where we really are in relation to each other, and discuss with each other on the basis of truth and not polemics and stereotypes.
The SAS, in my view, is simply the recognition of the position where we are at when we meet each other. It does not guarantee or necessitate union. But it does preclude false accusations and stereotypes and requires a more careful and accurate tone of discussion. There are lots of EO I meet who think I am a heretic, mostly Western converts, but that is their ignorance, it should not be allowed to set the tone of our general response to the wider mainstream communion of EO.
When Archbishop Gregorios and Metropolitan John attended the consecration of the Syrian Orthodox Cathedral in London they did not come as visitors to group they had nothing in connection with. And when Archbishop Gregorios asked that the Holy Spirit would descend and fill the place as it was used for worship I did not sense he was saying things he did not mean. Indeed he said that they were from his heart. This is surely a working out of the fellowship that many feel between the EO and OO, for all of the difficulties which Chalcedon still represents.
Our opposition to Chalcedon remains rooted in the events surrounding it, as is reasonable, but when we meet with the EO we are doing so on the basis of Chalcedon corrected by Constantinople 553. We must be clear which Chalcedon we are dealing with. It is a little like some atrocity happening in a war, the war continues and a peace is brokered and relations become friendly. When thinking about the atrocity there is always a need to preserve the condemnation of what happened, but when dealing with the relations with the other country, though the atrocity will need to be dealt with in due course to normalise relations, it is not helpful for it to be the only means of describing that other country, especially as time passes.
It is a little like me always saying to a Frenchman, 'We will have nothing to do with you until you repudiate the Norman Invasion of 1066!'. Chalcedon is more important than that. But it is how we are being encouraged to act. The Frenchman might say, 'What about our co-operation in the First and Second World Wars? Doesn't that count for something?'. And surely it must even if it doesn't take away the hurt and offence of the Norman Invasion. We would have to deal with the Frenchman through the prism of the co-operation in the First and Second World Wars, even while we still consider the Norman Conquest as an event in its own time. Of course if the Frenchman laughs at me and says 'I spit on your bowler hat, we humiliated you in 1066 and you deserved it' then a response might be different.
But my general point is that there is a difference between an historical event in its context, and the ongoing development of the belief of a group which considers that event important but which also moderates and changes its view of that event. They cannot be treated as the same.