Having colour corrected the whole 2004SE Jedi myself, I assure you that the lightsabres aren't a screwup in themselves, it is the overall colour and brightness issues that cause the lightsabres to look like they do.
Look at this clip of ROTJ lightsabre fight comparison between the 2004SE and my PDE. All I did was adjusted the contrast brightness and colours, I didn't rerotoscope or anything.