However when you divide the impact you recover faster and you get to put your enemy into a grapple (Dang those Tonfa)
Also the attacks don't have "half the force" due to balance. They would have even more force then a single handed weapon.
Let us review Newton's second law.
Force = mass * accelleration.
Or, more to what we are talking about with an impact, its derivative:
Momentum = mass * velocity
If the attack style you have chosen is "leap at an enemy, weapon first", then the amount of momentum behind this attack will be the sum of the mass of your body, weapon, clothing, etc. times how fast you are leaping at your enemy.
Read this next sentence carefully: This does not change whether you are sticking one weapon out in front of you or two. (Aside from simply having more mass due to an extra weapon, and probably less velocity to match, due to having to chemically generate that force to make that velocity in the first place. These effects are largely negligible for what we are dealing with, however.)
The momentum that you are applying, if you have two weapons, is therefore divided between the two points of contact that these weapons are impacting the target with. (The same amount of momentum is hitting, but you are dividing this out against a larger surface area.)
This is why hitting someone with two weapons at once by leaping forward at them is like firing two arrows from one bowstring - you are only generating so much force with your body, and then you are dividing it between two points of impact. If you want to penetrate an opponent's armor and body, you want to minimize the area of impact per unit of force.
To give another example, this is why someone can lie down on a bed of nails - nails are sharp when there is only one of them, but when you have thousands of them, you distribute your load over so many that you are not generating very much pressure over any one nail in particular.
This is why the notion that leaping forward with two daggers should let you deal the same amount of damage as swinging a battleaxe twice at the same time is pure munchkin mechanics.