So, this all gets down to physics - inertia primarily.
following assumes braking to a wheel-lock
When you brake heavily, front only, the rear will try to lift, this will reduce traction of course on the rear, but the broken traction on the front (in a non-ABS scenario) also results in reduced or zero ability to steer or control the front as well.
Conversely, rear-only braking causes the weight to roll forward again. This will result in aggressive changes in your steering and suspension dynamics, but ultimately you'll still be able to steer. Now again, in a non-ABS scenario, the total loss of traction on the rear will cause the backend of the car to swing much more wildly when front end steering adjustments are made.
would a skilled race driver benefit or would it make the car more dangerous to drive?##
Both. A very skilled driver could benefit slightly, but the hazards far outweighs these possible benefits. This is why (even in the manufacturer prototype racing circuits) they use computer controlled or static set systems - and mostly static from my understanding. You don't really need to be actively changing the braking dynamics, just set them correctly and use them right and you're good.
Moreover, I doubt even the best drivers can make the instantaneous braking adjustments needed to take advantage of independent braking systems.