When i play (monk) I usually run with 2 other monks and a DH/wiz and we dont really feel any issues with dps. On the contrary, it feels a little overpowered with the amount of buffs monks can give each other and ofc other party members.
We can do t4-t5, although t5 is not worth it yet. We have pretty ok gear, around 850-1100k dps on sheet and additional lightning damage. One of us is a little better geared with Odyn son and a Thunderfury but overall we are ok (but with plenty of room for upgrades).
When running higher torments we use Boon of inspiration + Time of need for massive mitigation, and the shields on activation of mantra actually stack which means we can last through most things. Combined with a legendary helm with 30% blind, lashing tail kick with blind, Exploding palm, Conviction with overawe, Deadly reach with scattered blows (some CC from the mobs jumping around and taking aoe dmg also), Unity etc. Those of us shielding run desert shroud to be able to keep shielding while taking massive damage. T3 and below we just use one shield and switch to another mantra instead for more damage.
The amount of aoe we do is insane and survivability and crowd control is also really great. Only thing we really lack is strong single target dps but that is not really a major issue. But CC mobs and letting aoe and exploding palm kill them...
The feeling I get with our setup is that if monk damage is buffed it would be overpowered.