Yeah, it seems to imply that the New Republic’s territory and influence seems to be limited to the Core worlds, at least in the five years after the Battle of Endor.

Regarding the Mandos, I also am not sure why certain Mando enclaves are in hiding despite the Empire having fallen years ago. I’m wondering if a rival faction of Mandos (or an Imperial warlord?) are in control of Mandalore, but they (like the Death Watch) are still in hiding. Or maybe they follow a certain nomadic tradition and their small numbers resulting from the purge is what compels them to stay underground for the time being. I’m guessing we’ll learn more as the show progresses. In Rebels, we see that the Mandos were starting to unite to take on the Empire, but this show sort of implies that their rebellion may not have gone well.

Boba was never in Rebels, but according to the new canon, Boba Fett never was technically a Mandalorian, but only wore the armor, so he had no allegiance to Mandalorian culture.