It’s not a genuine flaw. Story “rules” are not set in stone, and the set up of the lightsaber need not be so strict as to require the lightsaber be involved with its pay off. By which I mean, the lightsaber sets up the Force and Luke wanting to learn it. Then we see him using it to train with the remote. The ultimate pay off is him using the Force to destroy the Death Star. It doesn’t involve the lightsaber sure, but you can draw a straight line in terms of narrative purpose from the saber’s intro to the climax. The article misses the point of Luke’s training, it’s not about him mastering the saber, it’s about him letting go and using his instincts.