I think Lucas abandoned that idea they were heavy. Katanas aren't heavy and the lightsaber is pretty much a space version. I didn't think TFA was OT dueling at all. It was much faster and looked like they kept the Prequel speed, but took out all the flashy stuff.
I always felt that the highly-charged energy of the light beam coming out of a lightsaber made it difficult to wield. Luke and Obi Wan mostly use two hands to wield it in the OT. Vader uses one hand, but he's strong AF. I would definitely not equate the weapon to an inert sword like a Katana,
As for TFA, I agree that the dueling was not a total return to the OT style. But I disagree with you it was the same speed as the PT, only missing the flashiness. I think it was slowed down, and I'm betting, that the actors were told to fight like it was heavier than it appeared in the PT, and more like it did in the OT. So, not a total return to OT dueling, but somewhere in between OT dueling and PT dueling, but closer to the OT style/speed. It certainly jumped out at me, and as I said earlier, the change was one of the few things I admired about the film.
The Wook