I’m not sure that ?? ?? ??? ????? is really grammatically correct, but in any case what is the idea conveyed in that line of Tefillah? According to the Sefardim, it is that Hashem hears the tefillos of all people, and according to Nusach Ashkenaz, that Hashem hears the tefillos of Klal Yisrael. But what’s added by saying that He hears the prayers of “every mouth of His nation Yisrael”?
As far as Kegavna, it is a highly esoteric section of Zohar. I doubt 1% of those who say it really have any idea of what they’re saying. So the fact the Ashkenazim never adopted it is not at all surprising. Compare it to Berich Shemeih, which is also a section from Zohar, but has made it into almost all Ashkenaz siddurim in the past 300 years, perhaps because its simple meaning is easily understood.