I don't think anyone is saying that Orthodox Christians in the West need, or ought to be Western Rite, and if they are saying that, I would be the first to disagree with them. I know many Westerners who are at home in the Eastern tradition of the Church, and every single Western Rite Orthodox I know would "go East" before reverting back to whatever it was they were before. Orthodoxy is Orthodoxy.
This "essentialism" you mentioned is often found in certain narrative thrusts of WR literature, but I think it's easily overlooked that most of the main events that brought about contemporary Western Rite Orthodoxy took place in a time much different than our own. Orthodoxy wasn't much of a presence in "the West" a hundred years ago, and someone looking to convert would have a hard time finding parishes that would welcome them, and provide any kind of service in English, etc. So there was indeed a time when any Westerner looking to join the OC found the most promise in a Western Rite.
I would say that is no longer the case. And the more "the West" drifts from its ancient Christian roots, and the more Western Christians at large embrace non-traditional, non-liturgical expressions of Christianity, the more converts to Orthodoxy will find the Eastern Rite less and less "foreign." Or at least as equally foreign as the Western Rite.
So I think you are largely correct, Iconodule. But I did want to point out that there is another way of looking at the purpose and mission of the Western Rite that isn't focused on the not-being-Eastern side of things, and I think you find this in the "conversation" as well. And that would be that the Western Rite largely exists to preserve the wide catholic heritage of the West (all that is consistent and consonant with Orthodoxy anyway), and to further nurture this ancient, living tradition within an Orthodox context. The emphasis here is in a positive direction ("Let us preserve our authentic, Apostolic heritage") rather than a negative one ("I sure don't want to become an Easterner").
And it is in this sense that I also think you are correct in that the vast majority of people who will likely embrace the Western Rite will be those who have inherited said tradition; Anglicans and Roman Catholics. I don't see anything wrong with this, and it makes sense, does it not? Indeed, the way the AWRV was set up, this was the only way possible to be Western Rite; you had to be an already existing parish, coming into Orthodoxy as a whole. Who else could this have been besides formerly Anglican/RC churches?
Numbers and size shouldn't really be a concern, in my opinion. The validity of the WR isn't dependent on how many people convert. Orthodoxy as a whole is likely going to remain on the periphery of the Western religious landscape, despite any recent gains in the last half century or so, anyway. We should be thankful that we can be Orthodox at all, and rejoice in whatever tradition the Church has blessed us with.