I will check my notes but if memory serves, The 744 autobrake selector scale equates directly with the pressure supplied to the brakes. eg. AB1 = 1200psi, AB2 = 1600psi, AB3 = 2000psi to RTO = 3000psi. The rotary switch could just as easily read pressure rather than 1 - 5. Perhaps this is why a greater AB selection is used on wet runways on the Boeing...
(ref AMM auto brake test)
Once the correct conditions are seen, A/C on ground, wheel spin up etc the autobrake supplies equal pressure to all brakes as dictated by the selection.
The anti-skid does the rest until the brake peddles are depressed overiding the autobrake module.
Therefore if the T/Rs are used the aircraft pulls up at a faster deceleration than without, at the same auto brake selection.
The Airbus on the other hand is a completely different story.