Who gets to call themselves Mandalorian seems to be a matter of perspective, even in-universe.
This cult seems to follow an ancient creed which says "Mandalorian = Anyone sworn to The Creed of The Mandalore."
The government of Mandalore under Satine (and probably under the Empire too) obviously didn't hold this view and took the position "Mandalorian = Citizen of Mandalore or one or it's protectorates."
Death Watch's thing was less about following "The Creed" and more about using it's trappings to regain power for the warrior caste, presumably putting the workers and merchants back as helots where they belong, because that's how a warrior culture do.
We don't yet know what the deal is with the Fetts. They could just be wearing the armour and weaponry of a Mandalorian Supercommando simply because it's the best armour and weaponry around and it's distinctive enough to instantly give cred to anyone wearing it.
This cult seems to follow an ancient creed which says "Mandalorian = Anyone sworn to The Creed of The Mandalore."
The government of Mandalore under Satine (and probably under the Empire too) obviously didn't hold this view and took the position "Mandalorian = Citizen of Mandalore or one or it's protectorates."
Death Watch's thing was less about following "The Creed" and more about using it's trappings to regain power for the warrior caste, presumably putting the workers and merchants back as helots where they belong, because that's how a warrior culture do.
We don't yet know what the deal is with the Fetts. They could just be wearing the armour and weaponry of a Mandalorian Supercommando simply because it's the best armour and weaponry around and it's distinctive enough to instantly give cred to anyone wearing it.