I understand that you are Catholic. I have no problem with your choice.
I’m not Catholic or Protestant.
Here is how I would answer your concerns.
“If he refuses to listen to them, tell it to the church; “
Physical local expression of the Universal Church. A local gathering of those who have received the Gospel of Grace and gather to fulfill the purposes commanded of believers.
“The Church of the apostles was definitely one”
Still is.
“Paul linked this unity to the Church’s common Eucharistic bread”
Still does.
“Jesus had promised at the outset that “there would be one flock, one shepherd” (John 10:16).”
Still is. He is still the Great Shepherd.
“Would Christ establish his Church – to teach the way, the truth – and allow thousands of interpretation as to what is the truth?”
He didn’t. The Gospel of Grace is always the Gospel of Grace.
He is more than able to police His Church - even removing them when necessary - as Revelations shows.
You worry about so much br’er.
I'm just seeking the TRUTH.
You seem comfortable with multiple versions of the truth. I simply can't accept that.