Comes down to this:
Do you think Peter was the leader of the Apostles or not?
If Christ set up his Church like that, then its safe to say that the next generation of Apostles also had a leader....and the next and next.
By what name shall I hail thee, Martin? Shall I call thee the glorious leader for all the Orthodox Faith? Shall I call thee the holy Coryphaeus (Head), the leader of Divine dogmas that speaketh no errors?" (Byzantine Liturgy for the Feast of St. Martin, Pope of Rome).
In 680-81, the Ecumenical Council of Constantinople III calls Pope Agatho "the Head of the Church." And while this same council posthumously condemed Pope Honorius I for "heresy" (that is, for "assisting in the base assertions of the heretics" by not immediately condemning the Monothelites), it was clearly understood that Honorius was merely negligent and that he did not directly promote the heresy or speak with the authority of Rome. For example, Pope Agatho himself declares:
"The heretics have followed some passing expressions imprudently set down by one Pope [Honorius], who made no appeal to papal authority, nor to tradition from St. Peter. Against this I put the repeated, the continuous protest of Pope after Pope, authoritative, grave, deliberate. Their voice was intended to be, and was, the voice of the infallible Roman Church." (Mansi, v. 11, p. 285).