I had this thought as well. I justify it by saying that in a culture that is able to design and develop a brand new armored space station more powerful than your first in like, six years, it's safe to say technologies advance quickly. As for the Vader thing, I never really thought that he meant building a lightsaber was a uniquely Jedi skill. I always just thought he meant that building your own weapon was a right of passage for a Jedi. Simply a weapon for the masses, the lightsaber is more symbolic for the Jedi, part of their soul. As the galaxy becomes more reliant of blasters and laser-projectile weaponry, the Jedi continue the use of lightsabers, because it is part of their soul, such as the katana is for the samurai. So the Mandalorians would use very clean, mass produced lightsabers, very phantom menace-y in design. And that would be juxtaposed by the Jedi's lightsabers: unique to each individual who constructed it, more revenge of the sith/OT in design.