Although St. Maximus the Cofessor appealed to Rome for support, Rome did not have the authority to unilaterally make the decision on the matter of Monothelitism.
That bishops around the world appealed to the head must suggest that he had the power to repeal, reinstate or affirm because he was for those who sought him out a final arbiter (even in matters ecumenical the final arbiter was the pope, i.e., without his ratification a synod could not be considered ecumenical because not only was he the only patriarch of the West, but because he was head of all the Churches). Also, the pope’s cooperation in some shape or form had to be evident during an ecumenical council, usually in the form of papal legates armed with directives and definitions of faith, which were affirmed by an ecumenical council, and that in turn finally ratified by the pope (we come full circle). That being said, you have this odd notion that just because our pope can define a dogma or has universal jurisdiction, which ultimately derives from Christ’s commission to Peter to strengthen the brethren, that he needs must act alone rather than through an ecumenical council. Make no mistake, however, popes had the power to resolve doctrinal issues without issuing a council per se, for example, Pope Leo’s epistle to Flavian which definitively outlined the two natures of Christ was accepted in the East before Chalcedon even took place, i.e., it was not necessary to summon an ecumenical council. in fact before Patriarch Flavian (Constantinople) died, he wrote to the pope concerning the heresy of Eutyches in this manner:
"The whole question needs only your single decision and all will be settled in peace and quietness. Your sacred letter will with God’s help completely suppress the heresy which has arisen and the disturbance which it has caused;
and so the convening of a council which is in any case difficult will be rendered superfluous."
Only an Ecumenical Council had the authority to make doctrinal decisions binding on the whole Church.
An ecumenical council has binding authority on the whole Church when the only Patriarch of the West and the head of all Churches ratifies it. Moreover, as mentioned above, an ecumenical council is not always necessary in order to resolve doctrinal issues, the acceptance (signatures) of the Eastern bishops of Pope Leo’s definitive epistle was enough to resolve the issue. That a council was issued anyways was due to a misunderstanding:
The Eastern Church had been disturbed by the teaching of Eutyches since immediately after the Council of Ephesus (431) and the Nestorian troubles. In 448 Eusebius of Dorylæum had accused Eutyches and his formula “one nature after the union” (metà tèn ‘énosin mía phúsis) at Constantinople. Dioscurus of Alexandria had taken up the cause of Eutyches, and had condemned Dyophysism at the Robber Council of Ephesus in 449 (for all this see MONOPHYSITISM). Pope Leo hoped for a time to restore peace without another general council (his letters to Marcian, lxxviii, to Pulcheria, lxxix, and to the Patriarch Anatolius of Constantinople, lxxx). But meanwhile Marcian, acting on Leo’s former proposal, summoned a council on 17 May, 451, by letters addressed to all the metropolitans of the empire. It is clear that he acted on a misunderstanding, and had not yet received the pope’s later letter (Hefele-Leclercq, II, 639). Leo then accepted what had happened, and appointed as his legates Paschasius, Bishop of Lilybæum in Sicily, and a priest Boniface (ep. lxxxix; Mansi, VI, 125).
newadvent.org/cathen/09723c.htm
If Pope Martin I had the authority that modern Popes have, he could have simply issued a Papal Bull and settled the dispute. But the ancient Popes only had a primacy of honor. Thus, the decision on Monothelitism had to be made by the 6th Ecumenical Council, Constantinople III in 680.
In fact, upon becoming Pope, Martin I held a synod in the Lateran (105 bishops were present) to resolve the issue of monothelitism by sending the decrees issued at that council to the bishops and faithful throughout the world, including an encyclical he had written. The machinations, however, of an heretical emperor and patriarch (Constantinople) prevented the pope from resolving this heresy. He was captured and died in captivity (martyred for his orthodox faith) because he would not approve/sign the “typus”.
to be continued . . . . with Vigilius (whom Justinian held in captivity for more than a decade because the pope refused to ratify the decrees of the 5th council).