Dual-wielding does not mean you attack twice as often. There is a slight attack-speed benefit, but this is apparently being offset for you by the lower damage from the offhand weapon.
According to this thread on the forums, the formula for number of attacks per second is
((Main Hand APS*1.15) + (Off-hand APS*1.15))*1/2
Which means that if you had two identical weapons, dual-wielding would give you a 15% attack speed bonus.
The main reason to dual-wield is that you get the bonus attributes from both items. This doesn't mean much early on when attributes aren't very strong, but is a big incentive later on. However, compared to a two-handed weapon that does more DPS, there isn't a clear winner. It will mostly come down to whether you've found better one-handed weapons or two-handed, and what your preference is for faster attack versus stronger attack.
Updated Answer
Having soloed inferno recently with a dual wielding setup on my monk, I can now say as a fact that dual wielding is absolutely possible. But note, this highly depends on having two great weapons to use on your monk.
Here are the main advantages for dual wielding over a shield:
- Additional socket on weapon for HUGE critical hit damage boost (This is the most important factor, I've severly underestimated how much DPS having more crit hit damage can provide with modest crit hit chance (~30%).)
- A ton of more stats
- More Life On Hit Proc (This is the second most important factor)
- 15% faster attack
- 15% more dodge
My primary weapon right now is a ~850 dps 250dex 250vit 500 life on hit axe.
My secondary is a ~750 dps 850 life on hit 97% critical hit chance axe.
The main goal of this setup is to have high dps with huge life on hit and high critical hit damage. I'd prefer my primary to be socketed to have even more critical hit, but those weapons with similar stats to mine are too expensive right now and far beyond my reach.
Now that I have 3x more DPS than the old tank build, even though I'm down quite a bit on defense, its easier since I kill them faster so I don't have to tank as long. Also, the really deadly effects such as arcane turret and ground effects can't be blocked anyway, making blocking less useful than killing the target faster.
Finally, dual wielding axes is major style points, imo looks much nicer than axe/shield ;)
Old Answer
This answer is still applicable since having 2 great weapons is really really expensive compared to 1 and a shield.
From my experience, a shield is extremely necessary in late game inferno and ponies (the 1.03 damage nerf has made shield even better by reducing the spikiness of damage). Lets compare and contrast:
Shield Benefits
- 1000 - 1500 armor (double that if you use deadly reach)
- 70-140 resist all (70+ res all and another element of choice for stacking)
- 30-40% block (high block shield with JL + HoC) for 3k damage (note this is after reduction!)
- 1 free passive slot (you don't have to take guardian's path so you can devote 1 more passive for defense, such as resolve)
Overall, you gain HUGE damage reduction benefits for 1 equipment slot. If you are trying to be a tank this is almost a no brainer.
Duel Wield Weapon Benefits
- 15% Faster attack speed for more LoH
- More stats (weapons can get higher stats than armor can), and more unique effects like transcendence (having 100+ life per spirit spent is a great way to heal).
- Faster spirit regen (even faster if you have 2 spirit regen weapons)
- 15% dodge (if you take the passive)
Overall, you gain a little dodge (doesn't work when frozen, etc, and you can't dodge ground effects like desecrate and plague, which are the main sources of death in late game inferno), some more potential sources of healing and spirit regen, more damage, but way less survivability. Either way you won't be a tank.
To summarize, using a shield is a lot more defensive oriented, and thus provides the most survivability in late inferno acts (3+ and ponies). Not to mention finding a good shield is a heck lot cheaper than finding a good 1 hander with high damage, ias, stats, and LoH. You might be able to get away with duel wielding up to act 2, but I wouldn't expect you to last long beyond that unless you have godly gear and weapons.
Best Answer
In short, yes, 2H+Shield is still viable, and is in fact better now.
As Adesse pointed out, crusaders cannot dual wield, so you are stuck with a weapon+shield set. That being said, it is true that now using a 2H weapon with a shield causes a -20% penalty, but even before the patch the damage of a 2H weapon would have compensated for the penalty, meaning that 2H+Shield would have still been a (slight) improvement.
Now, with a buff to 2H weapons across the board, the net result is that 2H+Shield crusaders do slightly more damage than before the patch.