Protestants (and many others) have a great difficulty conceptualizing the idea of what the early church was like because they can only relate to their own experience.
It is true that when the church was young, sometimes there was only one church in an area and the pastor there was the bishop. His elders (presbyters) would attend liturgy with him and concelebrate in some way. But it was these elders who were sent out to the other side of town or across the valley when things needed attention and the bishop couldn’t be there.
In a way this scenario can resemble some of the Protestant churches today, where they have deacons and elders in the congregation. But this protestant organization is merely a reproduction of what the have been discerning form their own study of us in scripture and they completely miss the sacramental function of these men .
Let’s remember that Thessaloniki, Corinth and Epheses would have only been single congregations at first, but later they grew into large dioceses.
What is the difference? Why did these small congregations grow into large dioceses then, while small Protestant congregations of today grow to a point and no further, actually remaining local institutions?
The difference was in the authority of the bishops (overseers/supervisors) It can be compared to the difference between a classroom and a village board meeting.
In the classroom everyone is there to learn, this wisdom comes down to them like a gift, the students have nothing comparable to send back up to the podium.
In the village board meeting (or condo association) every person in attendance has something to say about the proceedings. The authority there derives from below.
The Apostles expended themselves entirely to teach and preach, desperately striving to save as many as possible. There was no authority from below, we were (and still are) learners. The gifts from above are Holy Wisdom (Sophia) and the Sacred Mysteries (Sacraments).