While you gain fury when you take hits, if you want make a build with huge amount of defense, do you think it's will be disadvantageous because you will miss fury because you avoid and block every hits...
Do you think it's will be better to decreasing your armor to gain faster fury ?
We don't know how fury will relate to the amount of damage dealt to you. At least, I don't know that. So it might be that a 1 hit KO and a successful block both give you the same amount of fury.
Still, it's a balance of play-styles. If you like living on the edge you can lower your armour and such to gain more fury. If you like to hold out longer and be able to melee longer, which also increases your fury btw, you will be able to do that as well.
I don't think that a defensive/'tank' build is non-viable. Defensive skills will probably have a lower fury cost, since you want to cast them before you get into the fight, not while you're fighting.
but wouldnt it get kinda boring because dont you want to kill things as quickly as possible?
Try play D2 on hell that way with balanced gear and see what happens.
The game is supposed to be fats paced but this doesn't mean the enemies will be drop outs that never attack and you will kill then all the way you like.
At the moment every class have defensive skills to a certain extend (like crowd controls and scape skills) and imo this means you will have to play both defensive and offensive. At this point your build may specialise you in one side or another.