Couldn't agree more with your observations about achieving 100 flywheel or rear wheel bhp from an A12.

only thing I'd clarify in what you said is that gear ratio and wheel/tyre diamter influence the results. Gear just multiply the torque that's seen at the wheel by the dyno. It won't affect the power output because power is simply speed times force, and there's a direct correlation between the difference in torque caused by different gears and the difference in speed caused by the gears. So yes, the motive force measured by the dyno would change, but the power would still be the same.