We say - yes.
I have another one wonderful question: What is the purpose of Ecumenical Councils if they don't precise the Church's doctrine?
A council becomes Ecumenical when it is accepted by the Church as an Ecumenical Council. The first part of the decrees of an Ecumenical Council lists those councils it recognizes as Ecumenical.
Despite the papal claims, before the Western Schism, every important decision concerning doctrine and administration meant to apply to the entire Church was made by an Ecumenical Council, not the Pope. Like all other Bishops the Bishop of Rome was subject to the authority of an Ecumenical Council. When Pope St. Leo rightfully objected to the Robber Council of Ephesus of 449 which exonerated Eutyches of heresy, he lacked the authority to do it himself. He had to appeal to the Emperor and the other Patriarchs to hold another council to overrule the Robber Council. This is the Council of Chalcedon of 451. Significantly, the council did not accept the Tome of Leo just because it was written by the Pope. Instead, the council sent the document to a committee which studied it and pronounced it orthodox. Then after it was approved by the committee, the Council of Chalcedon approved it. When Pope Vigilius refused to accept the decrees of the 5th Ecumenical Council, Constantinople II in 553, the council threatened to excommunicate him if he did not accept the condemnation of the Three Chapters. Until he accepted the decrees of the council, his name was struck from the dipytchs, list of canonocal Bishops. Pope Vigilius finally agreed to the decisions of the council and was reinstated in office. The 6th Ecumenical Council, Constantinople III in 680 condemned Pope Honorius I by name as an heretic. There are those who argue that this has no bearing on the declaration of the Roman Catholic doctrine of papal infallibility by the 1st Vatican Council. However, that is not a valid argument because the concept of a Pope speaking "ex cathedra" did not exist at that time. The decrees of the 1st Vatican Council state that Rome has never been guilty of false teaching. When an Ecumenical Council condemns a Pope for teaching heresy, even in a letter to the Patriarch of Constantinople, Rome has been tainted by false teaching.
Fr. John W. Morris