The last two questions were answered “it is good” “lekatchilah”- so it is not a directive and you could act ‘keminhag hamakom”.
As far as davening ‘beyechidus’ being better than davening with the tsibbur without a hat (or even a jacket) this is truly an astonishing opinion and I daresay that something was lost in the translation (as these are not Rav Kanievsky own words)