Sure, a shield means always sacrificing damage for more safety, but you won't lose 300% damage, thats totally exaggerated. You will probably deal ~30% less damage, but you gain armor, blockchance and most likely tons of resi in exchange. So if you want to play a trap/grenade build and you want to use a shield, it doens't matter if you wear a sword or a 1handed xbow.
And stop comparing a DH with the Barb, that not working like that, at least not now.
Ok, lets compare OP build with this build: http://eu.battle.net/d3/en/calculator/demon-hunter#cRYhQU!ceY!bbcZbY
First of all, Windforce has 480 dps excluding quiver, with best quiver about 600 dps. The best melee weapons has about 280 dps, but let's be generous and say it's 300 for fun.
Just sheer damage wise, this will be the rough difference: Many targets
Melee DH spamming granades: 300 x 0.95 x 1,10 = 314 dps in aoe
My bow DH: (((600 x 0,3) + (600 x 1,15)) x 1,35) x 1,15 x 1,1 = 1486 dps in aoe, but you won't always be free from enemies within 10 y, so let's say 1200 dps in aoe.Single targets
Melee DH SPAMMING impale constantly (which will never be sustained, but we are so generous toward melee dh in our calculations!): ((300x 2,5) + (300x0,20)) x 1,1 = 891 dps
My bow DH: (((600 x 0,3) + (600 x 3,35)) x 1,35) x 1,3 x 1,1 = 4227,795 dps
Melee DH will have a shield with good armor and resist and 45% dmg reduction unlike my bow DH. My DH on the other hand will have twice as much range, double aoe cone (compare multishot and granedes) and about five times as much damage.
Melee DH is !@#$. I loved the idea when it was viable before, but as it is - it's %^-*.