The problem NST has was it would launch itself out of the arena as the weapon acted like a lifting arm the moment it went on its side. A NST style machine with a disc wouldn't have the same problems as it would be slightly harder for it to lever itself over the wall... I think. I doubt it would need a larger diameter weapon than NST but your weight management would be an issue with a large disc rather than a bar, not to mention the cost of making the weapon in the first place.

Another issue was that NST had bludgeoning heads on its weapon. It was superb at energy transfer but because it was horizontal it would waste 50% of the force and go flying. A disc with a cutting tooth would give you the ability to slice into a machine in the same place repeatedly without sending yourself out of the arena.

I say the Supernova style machine is a good option if built right. With the right balance, weight distribution, cutting teeth rather than bludgeoning heads and a lot of magnets I bet you could make a very potent machine.