Lit:
Your points are all historical. The fact that one of the only contemporary examples you can bring is the Mt. Kisco “old minyan” should tell you something. If you go back far enough, all chassidim davened Ashkenaz. Different groups probably switched at different points.
Anyway, ignoring the Chassidishe angle, Mt. Kisco is not a run of the mill Litvish yeshiva. Your original claim was that “Oberlanders” are definitively Litvish.