DaMoshe: Who do you think you’re kidding. You know as well as anyone that Modern Orthodoxy is split between the Left-Wing Modern Orthodox (LWMO) and the Right-Wing Modern Orthodox (RWMO). YU has both, both in the student body and in the faculty. Mr. Avi Weiss is as mainstream Modern Orthodox as anyone. He was a YU Rabbi and RCA member. He was with YU and the RCA as long as he wanted to be. They never threw him out. He only quit the RCA not long ago. Mr. Weiss’s so-called “synagogue” is STILL and official Orthodox Union shul and he an OU “rabbi”. The OO have always identified as MO, from long before the term OO even existed. And they’re claim to being MO is at least as strong as that of RWMO.
Furthermore, the LWMO is larger than the RWMO, in terms of adherents. This is mainly because the right of MO (which is still to the left of traditional Orthodoxy) split over the last 40-50 years, with most members either moving left to LWMO or completely irreligious or otherwise moving to the right, such as becoming Chareidim (most Chareidi shuls and Yeshivos in America have numerous former MO Jews.)