There can be only one. Of the many things Leo did that made him great, it was his attention to authority that really jumps out at me. He certainly establishes a hierarchy but it is a collegial one. Each bishop or metropolitan has control in his flock but he instructs that each should be prudent and not hasty and in the end turn to the Apostolic See in order to resolve disputes or be guided in their office.
Not vetting those who would lead was as dangerous as allowing those who would break with Tradition to have free rein (though reign may be as appropriate). The consolidation of authority in a collegial hierarchy allowed for a more catholic Church, one with consistency throughout. Whereas the people might put forth a candidate, the appropriateness and worthiness of that candidate might not be conducive to harmony and orthodoxy. Of course, the same may be said later when all appointments came from the top down.
Yet, without that tight hierarchy and a single, final authority (based, as he so rightly points out, in the office of Peter), many of the heresies that plagued the Church and the Communion would have sundered her.
It is the duty of that hierarchy to serve its flock, not the other way around. Leo saw that and required that Christ-like servant behavior of the bishops who held power over their flocks. Forgiveness and mercy should be at the heart of any servant.
Let us pray daily for our bishops and priests, that they may be able to serve us in love as Leo calls them to.
The brotherly love of our colleagues makes us read with grateful mind the letters of all priests; for in them we embrace one another in the spirit as if we were face to face, and by the intercourse of such epistles we are associated in mutual converse. But in this present letter the affection displayed seems to us greater than usual: for it informs us of the state of the churches, and urges us to a vigilant exercise of care by a consideration of our office, so that being placed, as it were, on a watch-tower, according to the will of the Lord, we should both lend our approval to things when they run in accordance with our wishes, and correct, by applying the remedies of compulsion, what we observe gone wrong through any aggression: hoping that abundant fruit will be the result of our sowing the seed, if we do not allow those things to increase which have begun to spring up to the spoiling of the harvest.
...Noble precedents must be followed with eagerness that we may show ourselves in all things like those whose privileges we wish to enjoy. We wish you to imitate your last predecessor but one as well as of your immediate predecessor who is known equally with the former to have both deserved and employed this privilege: so that we may rejoice in the progress of the churches which we commit to you in our stead. For as the conduct of matters progresses creditably when committed to one who acts well and carries out skillfully the duties of the priestly position, so it is found to be only a burden to him who, when power is entrusted to him, uses not the moderation that is due....
-- Letter VI to To Anastasius, Bishop of Thessalonica.
No Christian should lightly be denied communion, nor should that be done at the will of an angry priest which the judge's mind ought to a certain extent unwillingly and regretfully to carry out for the punishment of a great crime. For we have ascertained that some have been cut off from the grace of communion for trivial deeds and words, and that the soul for which Christ's blood was shed has been exposed to the devil's attacks and wounded, disarmed, so to say, and stripped of all defense by the infliction of so savage a punishment as to fall an easy prey to him. Of course if ever a case has arisen of such a kind as in due proportion to the nature of the crime committed to deprive a man of communion, he only who is involved in the accusation must be subjected to punishment: and he who is not shown to be a partner in its commission ought not to share in the penalty. But what wonder that one who is wont to exult over the condemnation of priests, should show himself in the same light towards laymen.
-- Letter X to the Bishops of the Province of Vienne.