They're all Mandalorian...from a certain point of view. It all depends on how old you are and what you remember first. The Mandalorian design and lore was built around Boba Fett and then extended with Jango.
Everything since then has been retconned to suit the latest narrative. I prefer that somethings are left to imagination,as the mystique is half the appeal...
Yup for me Boba will always be the original Mandalorian, regardless of whatever weird backstory was created for him in the prequels.
They're all Mandalorians....................they're just not allowed to run for President of Mandalore.