As mentioned drum brakes produce more brake torque then disc brakes, with the same amount of piston pressure.
The wedging effect is called self activation. The leading shoe is self activating.....the rear is not.
I'm really not too familar with the valve you speak of which kicks the rears in first.
Some other comments.
There is no aftermarket adjustable brake proportioning valves that will "swap in" without redoing the brake lines.
Also....one of the drawbacks of drum brakes is the cooling. They don't cool as well as discs so brake fade can be a rather serious issue.
I've got some stuff from my vehicle dynamics course that that shows the different brake setups and info on each. I can scan and post if people are interested.
BTW ciper, I got the ECU today.......I'll PM ya....