He didn't say their dogma or theology is wrong, but that they could be wrong about what the person they are condemning is believing.
So if contemporary historico-critical research clears Nestorius of "Nestorianism" or Patriarchs Severus and Dioscorus of "Monophysism" and the Church lifts the anathemas against the persons - not the heresies (even if in the end no one actually embraced them), then the ACoE could receive Ephesus and the OO Chalcedon, and the rest of the EO Councils, or should these simply be dismissed as fighting wind mills and straw men? St. Cyrill, St. Leo, St. Maximus, St. John of Damascus etc. were so many Don Quijotes?
If you see them as "Don Quijotes", and this troubles your faith, then I say you are walking on thin ice. I've provided some quotes by St. Dioscorus in another thread, and there's plenty of information about St. Severus in over the internet, and over many books. They never failed to teach the full humanity and full divinity of Christ, without division, without separation, without confusion, and without alteration.
It is not merely "contemporary historico-critical research" that vindicates the anti-Chalcedonian saints of our tradition. It is the life of the OO Church continually throughout centuries, through her practice, and her Church fathers' writings preserved for us. Therefore, if we present to you the writings of Dioscorus or Severus, and you can't find anything wrong with them, then "historico-critical" is not fair, isn't it? We have our defenses.
You have to understand that throughout centuries, the "ancient research" dominant in its days, usually Chalcedonian Western-European Christianity, were very biased. For centuries, they have research that "shows" the Pope of Rome was the head of the Church "unquestioned". Is it "contemporary historico-critical research" that refutes all these claims, or is it an objective seeking of truth based on real material from the Eastern fathers?
Likewise, the ignored Church fathers of the OO tradition also deserve to be taken a look at. Just because Western Christian scholars have lead us to think we are Monophysites does not mean it's set in stone by scholars.
As for Nestorius, in my personal opinion, based on reading what he wrote, he fails to clearly make the case that Christ is different from a prophet who unites himself with the Word. This isn't based on reading St. Cyril, but based on reading what Nestorius and Theodore of Mopsuestia wrote.