Let’s assume for the moment that episokopos in the Greek New Testament means “bishop.” Things get really interesting in the following passages:
Acts 20:28 Be on guard for yourselves and for all the flock, among which the Holy Spirit has made you [a]overseers [bishops], to shepherd the church of God which He [b]purchased [c]with His own blood.
In these two passages Paul is speaking to specific, local churches. I can grant for a moment that the Ephesian elders represented a multitude of churches in the Ephesian area. Perhaps. You still have many bishops within one church-area.