Could it be that boosted disc brakes are easier to operate, as in they take less pedal effort, this translates into ease of use, especially when in a panic situation? So, you stomp on them hard, they lock up, you back off and try again, because this is easier to do (less pedal effort) you can do it faster and more controlled, and that's where the better stopping distance comes from. Not the fact that the wheels lock up easier, but that they are more easily controlled between lockups?
I don't think you are asking the right questions, you seem to think that if the wheels can be locked up on two completely different brake systems then they are effectively equal?
I think not. I drove my 52 1 ton with stock brakes, they seemed fine, and I had no problems with them, never worried about it.
Then I switched to hydroboosted disc brakes on the same truck, and I can't begin to describe the difference. Almost look at the peddle and the truck would stop, and quickly.
What ever the difference I soon found myself driving harder up to a stop and braking harder in the last moments, not good things, but the brakes were different, and I unconsciously took advantage of that.
Grigg
