Lorewise, in the original movies, they were supposed to be heavy.Doctadoone said:The thing I found most, shall we say annoying about the fights, is that when they swung the lightsabers, it looked like a broadsword. As in, it had a heavy heft to it. Lightsabers, lorewise, were so light and so unlike other melee weapons, that they took so long to master. I think they had it backwards in the movie, the swings were slow where they should have been fast. If they wanted to show inexperience they could have swung the blade too far, leaving themselves open.
TLDR: The swings should have been much faster for the weight of the weapon, they looked too slow.
Skip to 3:30, and you'll see Mark Hamil and George Lucas talking about how they were supposed to be wielded like massive 2 handed swords.