I think the New Testament, as a whole, lays out what the church is and how it should be, and that the closer we follow the New Testament the more we can fulfil the church's mission, which includes safety for its members including proper discipline, encouragement, and admonishment.
I think that when we stray from the New Testament, the church doesn't work as well. One obvious example would be when the church merged with the state. But another example is in the Protestant era when "church" became some kind of vague ephemeral invisible thing, or just got redefined to mean "all people who are Christians anywhere". It's hard for a vague thing you can't see and certainly have no hope of ever attending to live up to the New Testament ideals laid out for it.
Ultimately I'm not sure what the purpose is of these interrogations, though, like it's some kind of "gotcha". Obviously I believe in a united, undivided church of God, and a one, true, visible church. It is not some big secret that I believe these things. I think all other Christians should embrace these things as they are found in the New Testament; if that isn't convincing, then I recommend reading early Anabaptist writers, who expounded upon the same things.
If you don't think your own congregation is the true church, I feel you should do one of two things:
- push for changes to make it part of the united, undivided church of God, in unity and harmony with all other true congregations of the true church.
- give up and leave it, and search for the true church elsewhere.