Acceleration is the result of force on a mass.
Power is the product of force and the distance moved (per second).
So, altering the gearing for acceleration gains you rear wheel torque (force at the contact patch), but you lose a corresponding distance travelled. So the power is the same.
Except… altering the final drive gearing for better acceleration will cause the loss of some power as seen by a dyno.
Firstly, it takes more force to turn the chain through the near 180º angle at the front sprocket because the radius of that turn is smaller with a smaller sprocket. Also, at any given bike speed, with a larger rear sprocket the chain will be travelling faster than it was with standard gearing so more chain length per second has to go round that tighter turn. Obviously, the lighter the chain is, the less energy is lost that way (one of the reasons belt drive is good).
Secondly, the energy lost at the tyre contact patch will be greater… more force means more deformation and slippage (not meaning a burnout situation, there is a small amount of slip in normal acceleration).