The Avesta community is headed by a Parsi Zoroastrian and most members are Parsis too. Yes, unfortunately they can be quite dogmatic.
In the U.S. there is the Federation of Zoroastrian Associations of North America. There are other Z associations and communities in U.S. and Canada too. You’ll find their views are much less dogmatic.
Not that I engage in debates with organizations via e-mail, I thought the same as your earlier point about the first members were converts as well but I didn’t really want that to be my first step. It’s sort of like suing a fraternity for membership.