The claim is well-grounded: the bestowal of the pallium is meant, in the Church’s own liturgical and doctrinal symbolism, to make visible that a metropolitan’s mission is both apostolic (rooted in the Church’s succession from the apostles) and unitive (expressing communion within the episcopal college under Peter).

What the pallium signifies in the Church’s own teaching

The Church presents the pallium as a sign with specific ecclesial meaning, not merely an honorific ornament. Pope John Paul II describes its eloquence as expressing:

• Communion that “gives every aspect of ecclesial life its shape,” and that this communion is “organic and hierarchical.”
• The Church’s need for the “special service of the Church of Rome and of her Bishop” as Head of the Episcopal College.

Pope Francis, in the rite’s context, explicitly frames the pallium as “a liturgical sign of communion” connecting the See of Peter with the metropolitans and “through them to the other Bishops of the world.”

So the pallium is not simply a marker of rank. It is a sacramental-sign (in the broad sense of a liturgical sign) that points to the Church’s structure of communion.

Why this underscores apostolic succession (not just “continuity of office”)

Catholic teaching ties the Church’s unity in faith and sacraments to apostolic succession. The Catechism states that the criterion for unity amid liturgical diversity is fidelity to apostolic Tradition—“a communion that is both signified and guaranteed by apostolic succession.”

It also teaches that bishops are the successors of the apostles, and that they are “the visible source and foundation of unity” in their particular Churches.

Connecting this to the pallium: Pope John Paul II explains that the pallium’s bond with the tomb of Peter is precisely what makes it a symbol of a deeper connection to Peter’s mission, so that metropolitans are called to build unity through:

• the profession of the one faith
• fraternal charity

In other words, the pallium’s symbolism is “apostolic” not because it is part of episcopal ordination, but because it expresses communion with Peter in the same apostolic mission that continues through successors.

How it expresses episcopal unity (communion within a hierarchical body)

The Church is not a merely decentralized federation of bishops; it is a communion with visible unity. The Catechism describes the bishop as receiving the fullness of Holy Orders, integrating him into the episcopal college, and making him the visible head of his particular Church. It also states that bishops share in apostolic responsibility and mission under the authority of the Pope, “successor of St. Peter.”

Pope John Paul II gives the pallium’s ecclesiological logic in a single phrase: it expresses that communion is organic and hierarchical, and that the Church is one in need of the “special service” of Rome.

Likewise, Pope Francis presents the pallium as uniting (through metropolitans) the See of Peter with the entire worldwide episcopate.

So your thesis—apostolic succession + episcopal unity—matches the way the Church itself describes the pallium’s meaning: it is a visible sign of communion that protects unity of faith and sacramental communion by locating metropolitan authority within the apostolic and Petrine structure.

A necessary nuance: the pallium is a sign and a legal authorization for metropolitan office, not the sacrament itself

It’s important not to confuse categories.

• The pallium is received by metropolitan archbishops as a sign of their pastoral mission and communion with Rome.
• The older Catholic Encyclopedia explains that (in general) the pallium is worn by archbishops and symbolizes their participation in the supreme pastoral power of the pope, and it notes that an archbishop who has not received it may not exercise metropolitan functions.

This helps clarify the “underscores apostolic succession” claim: the pallium does not create apostolic succession (which is guaranteed by Holy Orders and sacramental continuity), but it makes visible and guards the correct communion and lawful exercise of metropolitan authority—so that unity is not merely ideological but ecclesially concrete.

What you can responsibly conclude from the evidence

Putting these texts together, the pallium bestowal underscores apostolic succession and episcopal unity in three tightly connected ways:

1. Apostolic succession safeguards unity in faith and sacraments—the pallium points into that apostolic communion.
2. Metropolitan authority is ecclesial communion under Peter—the pallium unites the See of Peter to metropolitans and, through them, the bishops worldwide.
3. The rite expresses a hierarchical, organic communion—not only continuity of mission, but visible unity within the episcopal college.

Conclusion: The Church’s own catechetical and magisterial descriptions support your summary: the pallium is a liturgical sign that concretely manifests how metropolitan pastoral authority is anchored in apostolic succession and expressed as visible communion within the episcopate under Peter.