I always assumed that a lightsaber can be as good as a blaster, but one has to be really, really, good at it, to the point where Jedi are the only ones who can essentially pull it off and thus are still using them. In fact the difficulty in mastering it would be demonstration of what a light Jedi's path is, choosing a more disciplined, more challenging path as opposed to one quicker and easier. Plus the weapon embodies the classical idea of what a Jedi is supposed to be, a servant and protector of the Republic no matter how much technology and civilizations change.