I only reviewed the first link. What I took away from it is that furin cleave sites occur in the family of coronaviruses naturally, but have not been seen in those most closely related to SARS-CoV-2. This note about not having closely related coronaviruses having such a feature is also true of SARS-CoV-1, which also leads evidence to its ability to occur naturally within a given subgenus (unless we posit also original SARS was lab-leak, but I do not think anyone has posited this.)

I have not evaluated 2-7.