if you look at the second set of Equipment that is Level 20, and look at the Damage the Weapons do, you will see why affixes that increase DMG by % is less effective than those that increase it by +.
Hammer does the most damage of all weapons, with an average of 450 (337 - 562). in arena WD% is around +20% for Epic , +40% for Legend. so with Legend WD% you would get around 630 DMG. that 200% ED% you have would be around +40%, so now you are doing around 882 DMG.
450 + 1040 WD+ is 1490 DMG, add +40% ED%, gives around 2086 DMG.
450 + 1040 WD+ + 2080 ED+ (2 ED+ affixes) gives around 3570 DMG.
hope this helps.