How about this (needs more “pathos”, more about the general idea):

DD: Your people believe it is to be earned in combat, i know. But you did not loose Mandalore, because you accepted this weapon as a gift. You lost Mandalore because our tribes were splintered, caught in a cycle of fighting each other. Mandalorians have fought over beliefs, grudges and… this weapon. If the darksaber really is meant to be a symbol of our unity, we must not fight each other over it. It shall be a gift, given from one Mandalorian to another… one tribe to another… Because we are one people. Exiled from our home. Wouldnt it be our best chance to retake our home… together?

I think making the “rules” behind the darksaber a parallel to the Mandalorian infighting of the tribes has some potential. It also sets up the lesser importance of the weapon, making the unification of the tribes Bo Katans claim to fame.

edit:
As to the resolution of the Mandalore storyline. Since there is a good Armorer Model around, maybe a few scenic shots of Mandalore with a voiceover of her could do the trick? She could talk about how after the retaking of Mandalore and the destruction of the darksaber the tribes united in the belief in the Mythosaur and Bo Katan (who bears his symbol). It breaks the “show dont tell” rule, but since we have to work with what we got, it might be worth considering.