So because they have the same whp on a dyno, you think they have the same whp on the street in all scenarios, even when the drivetrain inertia, which influences whp, isn't a factor?
The STI just magically can hit 158mph, while the WRX can only muster 142mph, but they 'must' have the same whp on the highway because they have the same whp on a dyno.
Maybe this is a better anology, picture a bucket loader on a dyno... the whp will be read waaay lower than crank because what you're measuring is the acceleration of the rollers, which is being hindered by the acceleration of the masssssively heavy wheels, flywheel & entire drivetrain.
Now picture that bucket loader towing something, steady state drivetrain, power passing straight through. HUGE power making it out the wheels, doing work, because it's not being robbed by /invested into the dynamics of the system.
These scenarios exist in cars, like overcoming wind resistance, increasing elevation, etc and crank hp will play a bigger factor because drivetrian loss is playing less of a factor. And dynos cannot account for it. Crank horsepower is real power in the right scenario.