The fact that you think Obliterate does spell damage makes my BS indicator break.
DK's main damage supply in PvP = Frost strike, and all of the bonus damage is Frost Damage, which can be soaked. The fact that you then take 30% less Frost damage will make Nether Ward last longer and so possibly absorb more magic schools.Both hunters and DK's have a lot of physical damage coming out, so nether ward does not negate 30% of their damage.
You're putting a 3k arena sub rogue against a 2.2k BG DestroLock. They have completely different playstyles and thus are not compatible for comparison in a 1v1 scenario.As for reckful vs him as destro, have you seen the NA invitational? Reckful was locking down the afflic locks like crazy, and destro relies a lot more on hardcasts.