for normal characters yes.
Now the monk has a special line in his unarmed strike ability that says
"There is no such thing as an off-hand attack for a monk striking unarmed. A monk may thus apply his full Strength bonus on damage rolls for all his unarmed strikes."
So he does have the ability to 2wf, but they are all full STR attacks.
Just think of the weakened off hand as being due to stance problems (since a lot of the power in melee comes from the legs and core, actually)
Monks can be written off as having the training to be better with their stance, so the point that there is no loss of damage (the rest face at least some loss; even double slice doesn't help with the lowered power attack)