The Church's saints, hymns, and councils call them heretics. When it comes to this, it is that simple and I don't care about modern opinions. Picking and choosing what parts of the councils are legit and what are not is Protestantism in an Orthodox package.
Thr councils are clear who is a heretic and who is not. In fact, Constantinople 2 clearly states that to defend Theodore or Origen is anathema
We have Theodore Mopsuestia and Origen being written about positively by Orthodox today. One theologian did not see Theodore as a problem when understood in context. I suppose Origen made heresies, but he is still called a doctor of the church or some other positive title.
Personally, I am ok with calling Dioscorus and other OOs who reject "in two natures" "heretics", if we can call deniers of "Theotokos" heretics.
But I also care about reuniting, as Paul instructs us to avoid factionalism, and don't think that everyone must fully accept every anathema and canon of every council to be Orthodox, because it's just a fact that some Councils' canons touching were never formally accepted by every EO church. It's not a matter of being uncaring Protestant or legalistic Catholic about canons, that's just a fact. To give an example, baptism is both theological and ritual in nature, but the OCA and MP does not rebaptize Trinitarian heterodox, unlike what one of the canons accepted at a council says.
Strictly speaking, EO churches have accepted the main faith statements of each council and also openly affirmed each council, but also have not always accepted every canon or decision by every council. Applying that model to OOs, it looks to me like we would require them to accept the council and the main faith statement, but the anathemas would be secondary.
I think once OOs accept the phrase "in two natures", that will incline them to look at their history differently when it comes to Dioscorus and Severus. Looking at the fact that Dioscorus was openly considered a nonheretic by some who deposed him at Chalcedon, and since EO churches don't accept every decision by every council outside the main formulas, it is hard for me to require OOs to do so. Not every saint or anathematized person in every EO church is considered that way in every other EO church. I think Ivan the Terrible was never excommunicated by Greeks, although they didn't have a reason to.
Requiring OOs to anathematize Dioscorus and Severus because the anathema was a Council decision raises two questions:
1. Were Dioscorus and Severus "heretics"?
This goes back to the question of whether denial of correct terms for mistaken
semantic reasons is inherently heresy.
Your answer appears to be that if a council decides something is heresy, then it means it's heresy.
If a council meets and cannot come to a unanimous decision on whether something is heresy, does that mean that the majority opinion about whether something is heresy is right? Ephesus II and Chalcedon were both councils that intended to be ecumenical and had majorities that took opposite opinions from each other.
It seems that not every decision by every council is necessarily fully correct, or else we wouldn't have divisions between EOs on Council decisions.
As I mentioned, at least one major EO bishop who supported Chalcedon's formula and who deposed Dioscorus but who didn't consider him a heretic, he debated this with the Roman delegation, which considered Dioscorus a heretic.
My guess is that it's a weird situation. Denial of in "two natures" is theologically mistaken, thereby heretical and implicitly in fact monophysite, but Dioscorus also rejected monophysitism.
So to 1. I would guess "Yes", but it's a conflicting situation.
2. Does every church need to accept every anathema of every council?
I think the answer is no. We know that there are Council canons that aren't accepted by every EO church, some are even rejected by EOs. We know that some EO churches don't openly accept all each others' saints or anathemas. And we know that there are Orthodox theologians and bishops who have considered Dioscorus and Severus to be non-heretics, including at least one who deposed Dioscorus at Chalcedon. And in practice it looks like churches don't impose every anathemas by the Ecumenical Councils. Can we really say that every person who denies any unwritten tradition is anathema per the explicit Council canon, for example?
These two major EO theologians and EO bishop disagree with the heresy charge:
"I support what Paul Verghese has said now. It is true that we have tended to take a position of conciliar fundamentalism (!). In the matter of tradition, continuity is essential…We should try to realize continuity. But I doubt if true continuity can be maintained on the level of persons. For example, take Leo and Severus. How do they stand in the communion of saints? Or take Origen. He was indeed in communion with many, but does not even a council proclaim him out of communion? I would suggest that all we can do is to consider individuals as models in particular situations." (Fr. Meyendorff, Metropolia, p. 34)
I would myself suggest that the anathemas served almost as caricatures, that is, as exaggerated presentations of the figures they ostensibly delineated which thus brought into relief elements of doctrine that all of us today would reject: e.g., the in fact inaccurate pictures of Leo as teaching “two Christs” and of Severus as effectively obliterating the humanity of Jesus. Surely, the final issue, the “bottom line,” must always be the actual faith that all of us, I believe, hold in common.
Bishop Alexander (Golitzin) of Toledo
This point may be illustrated by reference to what Chalcedonian Orthodox regard as the sixth ecumenical council, III Constantinople (681 A.D.), which proclaimed anathema to Dioscorus “hated of God” and to the “impious” Severus of Antioch. This council was faced by the heresies of monotheletism and monenergism, which held that there was but one will and one natural energy in Christ. As frequently the case when faced with a new challenge, orthodox churchmen on the one hand denounced these heresies as dangerous innovations, but on the other they tried to demonstrate that the new heresies were simply old, longcondemned heresies in disguise.
...
Hence, in the course of a long series of anathemas pronounced at the final session of the council, we find the names of Dioscorus (elsewhere described by the council as “hated by God”) and Severus (elsewhere characterized as “impious”). Clearly, by the time of III Constantinople popular opinion did associate these names with heretical positions condemned at earlier councils. And this tendency continues in later centuries. For example, hymnography for the Feast of the Seven Ecumenical Councils (July 16) can exhort the orthodox to “abhor” Dioscorus and Severus along with a multitude of other heretics.8 But these formulations – these “short-hand” notes from later times – in fact are very misleading.
...
Let us also consider the case of Severus. He clearly affirms the basic Christological truth that Jesus Christ is consubstantial with His Father in his divinity and consubstantial with us in his humanity. In other words, he does not fall into the heresy of Eutyches condemned at Chalcedon, which denied Christ’s consubstantiality with us and thus his full humanity. But Severus uses technical terms like hypostasis and physis in ways very different from the later formulations of Chalcedonian Orthodoxy. If read on his own terms, he is not guilty of either the heresy of monophysitism or the heresy of monotheletism as these have been condemned by the ecumenical councils.” His terminology may seem idiosyncratic,
Anathama: An Obstacle To Reunion?
Fr. John Erickson, former Dean of St. Vladimir's seminary
However, I agree with this criticism of Severus:
The “monophysite” position consisted essentially in a sort of “Cyrillian fundamentalism” which allowed no compromise at all. The Chalcedonian orthodox camp was making major terminological concessions and clarifications: the antichalcedonians were making none. Even the great Severus of Antioch, who saw the dangers of unabashed Monophysitism and understood the importance of affirming the full reality of Christ’s manhood, stopped short from accepting “two natures after the union”. Several individual leaders of Monophysitism eventually accepted Chalcedon, but they were disavowed by their flocks.
http://classicalchristianity.com/2012/05/19/are-the-non-chalcedonians-orthodox/
And I am aware that a canon of the 6th Council says this:
…[T]he Manichæans, and Valentinians and Marcionites and all of similar heresies must give certificates and anathematize each his own heresy, and also Nestorius, Eutyches, Dioscorus, Severus, and the other chiefs of such heresies, and those who think with them, and all the aforesaid heresies; and so they become partakers of the holy Communion. (Canon 95)
and the 7th council has a decree that says:
With the Fathers of this synod we confess that he who was incarnate of the immaculate Mother of God and Ever-Virgin Mary has two natures, recognizing him as perfect God and perfect man, as also the Council of Chalcedon has promulgated, expelling from the divine Atrium [αὐλῆς] as blasphemers, Eutyches and Dioscorus; and placing in the same category Severus, Peter and a number of others, blaspheming in various fashions.
So my conclusion is that "in two natures" and each main faith statement of the councils must be accepted, but not every canon or decision, ie. it's not necessary for OOs to also openly recognize him as a heretic. Since it looks to me like Severus was a heretic, semantic or not, by denying two natures, I don't know why it's necessary for EOs to lift their own anathemas. Further, once OOs do recognize that "in two natures" and "has two natures" are perfectly fine statements, it points them to reevaluating the writings of Dioscorus and Severus.