Did the sword cut Superman or his costume? And the sword is essentially using Supermn's own power against him.
As for Deathstroke taking Superman's punches, it does absorb kinetic energy and one can assume Superman was holding back to an extreme degree because he didn't know what the force field could handle and he didn't want to kill Deathstroke.
And yeah, Priest made it very clear that Deathstroke didn't have a chance in hell.
Well the first punch has the shield at 90% of it's design limit, the second 382% of it's design limit and the third by 9200% of it's limit.
So Superman was hitting around 102x harder by his third punch than his first.
I mean, just going by the scans anyways.