My answer is "yes and no", partly because it depends on the what exactly you mean by some of the words in your question...such as "natural" and "noble" and even "best" (best for whom?). In other words, I could argue for either "no" or "yes" depending on what exactly is meant by those words.
I would say that when a relationship is achieved about which both people are and remain enthusiastic and happy throughout their lives it usually produces among the happiest and most contented of human life experiences for both the people directly involved and for members of their immediate family (especially their children, if any)...so, yes, one might call such an outcome about the "best" one could hope to achieve. And I think the "out years", the situations and experiences of the people long years and decades after the pair bond first formed, are very important...weigh heavily in what one might reasonably mean by "best". Fwiiw, I don't think perfect monogamy is an essential component of these most rewarding romantic outcomes. Maybe they have to be perfectly monogamous to be considered "noble"...but I don't know what you mean by that word in this context.
That said, I think only a minority (but not a tiny minority) of people achieve that sort of outcome in their romantic lives, so I don't know that I would call it "natural". More common and thus, in my definition, more "natural" are relationships that fall short of such a perfect or idealized one in various ways. But this is hardly news...
-Ww