The Council of Nicaea and the following councils called by St. Constantine nowhere lay out a Biblical canon.
Pope St. Athanasius the Great, in his
Easter letter of 367 to his churches. However, this was not binding upon the whole Church, but merely his own Alexandrian Church. The heads of each respective Church, whether it be the Bishop of Rome, or of Jerusalem, or of Antioch, or of Alexandria, or of Constantinople, only had jurisdiction over their respective churches, and not over any other church.
You overlook the fact that these local synods often had slightly varying lists of books of the Old Testament. Some, for example, include Sirach and the Epistle of Jeremiah, while others don't. The fact that the Councils of Hippo and Carthage publish their own lists of books of the Old and New Testaments which are at slight variance from the Roman canon means that the Council of Rome was not seen as dogmatically binding on the whole Church. Trullo makes no reference to this supposedly "dogmatic" definition of the Council of Rome.
From Canon II of Trullo: "But we set our seal likewise upon all the other holy canons set forth by our holy and blessed Fathers, that is, by the 318 holy God-bearing Fathers assembled at Nice, and those at Ancyra, further those at Neocæsarea and likewise those at Gangra, and besides, those at Antioch in Syria: those too at Laodicea in Phrygia: and likewise the 150 who assembled in this heaven-protected royal city: and the 200 who assembled the first time in the metropolis of the Ephesians, and the 630 holy and blessed Fathers at Chalcedon. In like manner those of Sardica, and those of Carthage: those also who again assembled in this heaven-protected royal city under its bishop Nectarius and Theophilus Archbishop of Alexandria. Likewise too the Canons [i.e. the decretal letters] of Dionysius, formerly Archbishop of the great city of Alexandria; and of Peter, Archbishop of Alexandria and Martyr; of Gregory the Wonder-worker, Bishop of Neocæsarea; of Athanasius, Archbishop of Alexandria; of Basil, Archbishop of Cæsarea in Cappadocia; of Gregory, Bishop of Nyssa; of Gregory Theologus; of Amphilochius of Iconium; of Timothy, Archbishop of Alexandria; of Theophilus, Archbishop of the same great city of Alexandria; of Cyril, Archbishop of the same Alexandria; of Gennadius, Patriarch of this heaven-protected royal city. Moreover the Canon set forth by Cyprian, Archbishop of the country of the Africans and Martyr, and by the Synod under him, which has been kept only in the country of the aforesaid Bishops, according to the custom delivered down to them."
Now, if the Council of Rome was in fact a "dogmatic definition upon [the] Biblical canon" made by the "Catholic Church", then surely Trullo would have referenced it alongside its list of various Ecumenical and regional councils. The fact that it doesn't should tell you that Rome didn't call the shots as to what and wasn't canon for the rest of the Church.