Rainus: You cannot invent a new shita from a story about the Gra.
I have davened in KAJ-Beitar as well as spoken there on Fri night and I know most of the members personally. My observation, confirmed by one of the organizers of the minyan, is that the majority may have families that originated in Germany/Switzerland generations ago but few of them have fathers who wear tefillin at all. Would you like to go over the list of regular mispalelim name by name?
I have heard from numerous sources intimately involved in the Yekke shuls that Ramot does NOT wear tefillin CHM based on R’ Elyashiv’s psak.
My neighbor Deutch is a chossid of Erloi and tells me that his family and the vast majority of Erloi do NOT daven Ashkenaz. I still need to ask him how many wear tefillin.
R’ S. Z. Ulman forbade KS from wearing tefillin.
Thank you for the quote of R’ Yitzchak Karo. now I understand that “therefore…” in your original post was your own words and not a continuation of his quote. BTW, it a strange statement he makes to say that minhag sfarad follows the Rosh in all matters, any ba’al halacha knows this is not true.