Low engine vacuum? Bad check valve in the booster? 03 and 04 had a different pedal feel to them. Can't remember what made part made it feel different.

 

Check under your master cylinder for a leak. Mine was sweating, not even dripping yet, and my brakes SUCKED, almost hit someone.

 

I am also a physicist. You say you are one, but your posts are littered with the most basic misunderstandings. ABS did not CAUSE your vehicle to accelerate, because it is incapable of increasing the kinetic energy of the vehicle. All ABS can do is reduce the braking effort. It is possible for it to ALLOW the vehicle to accelerate, but gravity or the engine must be doing the work.

I would proceed by finding a shop with a brake dynamometer and simply testing the brake effort on each wheel. You could have one or more seized calipers or another fault which is causing a lack of braking effort.