Dream, your friend has a small displacement normally aspirated car. This is different than your car. Car's can loose a fair bit of power from not having enough back pressure but this is much more rare on a turbo. The turbo itself creates a large amount of backpressure which is usually more than sufficient for the motor. As for your friend, I would think that 2.5" would not be that big a problem but then again, I'm not a honda guy. If he's still got his stock piping, he could try that?
Dream, there's this thing called a high stall torque converter you can use with an automatic (they even sell em for your car). This is what enables cars to rev from a stop with an auto. This is what your dad is probably assuming is in your car (which it does not have).
2015 STi: Still Stock
04 STi, 04 WRX: SOLD