It's helpful to got back to Apostolic times
There's the way the Church is defined in practice by the Apostles -- Peter and his Apostolic brothers preaching on the morning of Pentecost --- one flock, one shepherd --- guided by a Council of Apostles (i.e. at Jerusalem), message and vision to Peter confirmed by the Holy Spirit --- message being sent out to all the churches under the guidance of the Apostles, and thence to the successors of the Apostles made so by the laying on of hands --- already understood as "the Church as a Whole" (Ekklesia Kata-holos) by the time of Ignatius of Antioch ---
OR--- Of course there are other ways to parse it. One would be, based on your own personal bishopless interpretation (by definition schismatic) or EVERYBODY's separate personal interpretation (which would be chaotic).
One reason why the local churches cannot be completely autonomous, is that the teachings of the Church --- that is to say, not opinions of this or that cleric, this or that theologian, but the officiai doctrines -- are authoritative; if they were not, Christ would not have told us to resolve conflicts among the brothers by listening to the Church.
The tagline is a quote from Jesus: Matthew 18:17
One reason why the local churches cannot be completely autonomous, is that the teachings of the Church --- that is to say, not opinions of this or that cleric, this or that theologian, but the officiai doctrines -- are authoritative; if they were not, Christ would not have told us to resolve conflicts among the brothers by listening to the Church.
You posit that "the churches cannot be autonomous, ... because the official doctrines of a larger assembly are authoritative."
Then you bring up local church discipline.
Local assemblies *following God's Word* in matters of church discipline need no Roman hierarchy to carry out the Word of God.
I've witnessed successful churches do this in person over (too many) decades.
In practice, very few churches are in isolation. Most belong to a fellowship of like-minded churches, who share a common doctrinal statement that each adheres to locally.