I didn’t want her building it, I just wanted it to appear, like Luke’s appeared.

As for treating it like a joke, I don’t feel that’s as out of left field as is being suggested. It’s being tossed to show that it’s not a holy object, and given where Luke is at spiritually makes the most sense for his character to do. Calling it a laser sword is quoting the original trilogy, and again echos the dismissiveness that fits Luke’s character. As for porgs playing with it, that’s no more silly that Luke about to stab himself in the face in A New Hope or Anakin’s previous lightsaber being chopped in half and Anakin treating the moment like his parent is gonna ground him for getting a bad grade on homework.