It comes down to what design mission is required. It would have been easy to install a higher powered variant of the O-360 in the G2 and increase all the performance parameters, but this would of led to higher fuel burn. However it's mission is training and minimal operating costs; hence the current trade off is to let the altitude performance go and keep the low fuel burn.
I've had heard rumours that there is a 165hp version of the engine in the works, for those wanting higher altitude performance and cruise speed.
We're drifting again!