he is merely stating the traditional role of the Primacy: head of the bishops, not head of the church.
Just like we have deacons and archdeacons, presbyters and protopresbyters, bishops and archbishops, there is a protoepiscopos. But just like the Protopresbyters is not the source and condition of the local parishes, the protoespiscopos is not the head of the Church.
What Rome eft is the normal office of honor and some limited authority of the protoepiscopos, a "president", to use a modern word, of the collegiate of bishops, not of the Church, whose sole leader as Jerome confess, is Jesus Christ.
Imagine a federation of hospitals whose board is composed of the directors of each hospital. There is a person who is the chair of the board with authority in that particular body. But the chair of the federation is still, director of only his own hospital.