who deserves the mandalorian tag

Oh, I should also mention that The Mandalorian seems to think he would never again be a Mandalorian if he took off his helmet in front of someone else, while Sabine took off her helmet in front of others all the time, as did members of the Mandalorian royal houses.

So, are all the leaders of the Mandalorian royal houses not Mandalorians? Or is the character literally titled "The Mandalorian" an unreliable source about Mandalorian lore?

Again, I think that the answer is that there are many ways to be a Mandalorian, and so there's no point to nit-picking this stuff.

@MightyWizard was also quite perspicacious when they noted:

Just because a Mandalorian politician denied that Jango was a Mandalorian, which is a completely natural thing to do considering the fact that Jango was actively working for the Separatists while Mandalore wanted to stay neutral in the conflict, doesn't mean that Jango wasn't a Mandalorian

If you want to fight about this stuff because that's fun to you, go for it. We're not going to ever be able to come to an agreement because

1) there are different definitions of "Mandalorian" and we haven't yet even selected which one to use.
and
2) The source material itself is contradictory, and there are both reasons for the characters in the fictional universe to lie and reasons why they might say something honestly which would be misunderstood by others not immersed in the proper context. This is how you get The Mandalorian saying "This is the way," as if no Mandalorian could ever remove their helmet in front of others because there is only ONE way, while undisputed Mandalorians took off their helmets all the time.