I just attended a conference in which one of the workshops was over the subject of the reformation and this very plurality that you observe. [yeah ... I know ... thousands of years of history condensed into a 50 minute workshop --it wasn't just the reformation but also included the Eastern Orthodox before that, and all the happenings since. The speaker moved fast.]
But something said there left an impression on me. The speaker [not himself of Eastern Orthodox persuasion] said he had taken his students to visit an E.O. church; and the architecture itself conveyed a message. They don't have statues like Catholics do, but they do have plenty of pictures depicting saints all through history. Standing there he was surrounded by saints all around and above; all staring at him. It gave one the impression that you were being challenged --or maybe cheered on. Your team is bigger than your own little church, and certainly bigger than just you. All these eyes are there as if to say "here is what we did to advance God's kingdom. Now you are on the field --how will you carry this on?"
Our speaker appreciated with us, then and there, how productive and even essential it is for churches to recognize their roots into this history and how much accountability that should help us to recognize. Even non-denominational churches who may in some ways try to distance themselves from all such heritage or lineage -- they still have it whether they recognize it or not. And we all do well to stay plugged in for that "larger than my own church" accountability and not run from it.
That doesn't, of course, answer everything about all our co-existing cousins of denominations or how or if they should all relate to each other. But recognizing our common roots in a very stout tree is a good start --even if we still argue about who is the true continuation of the main trunk all the way back to the beginning and who is a "branch off of" that trunk. But in the end I think all that squabbling will be shown to be silly.
I personally maintain that the shadow of our Savior falls across such a wide swath of us all that it is no respecter of denominational or even organized religious boundaries. Yes -- it is necessary to be in "a" or "the" fold in order to find counsel and grow in discipleship. But as regards salvation, I think Christ may truly be "salvation without borders" so to speak. Certainly not geographically or even religiously drawn up ones anyway.
God's Church would be impoverished, not strengthened; if it were to have a sudden "unity" thrust upon it as an end of all plurality. Let detractors and skeptics complain about that as they will. (Can you tell this is a protestant speaking?). Unity is always good as an aspiration -- and I enjoy and admire that in my Catholic brothers and sisters to the extent that they actually have it. But we who may not formally be part of that specific fold shouldn't die a thousand deaths over not having it. There are some good reasons for that too.