Respected Mufti Saheb You have mentioned that loud zikr in unison in musjids is somethimg that is not advisable or you have not come across. Does this include the loud zikr of the late Hazrat Moulana Yunus Patel (rahmatullah alaih)? For he used to in his majlis`s have zikr. His khulafa as well as many sheikhs have such zik. Jazakallah
This act of loud Zikr in unision in the Masjid is not proven in the Shariat. If anyone deems it to be a Sunnat then know it is a Bidat irrespective who does or did it.