Brake pressure is split front/rear. Prior to modern electronics almost all vehicles had brake proportioning valves attached to the rear suspension. More weight on the rear compressed the rear suspension and a lever would automatically adjust the amount of brake pressure to the rear axle. So if you had more weight - more of the braking would be done by the rear - where the weight was.

I'm not an expert on the brake system in the 4Runner but I am reasonably confident that it performs the same brake proportioning through the vehicle pitch (rake). The 4Runner has a set of sensors that measure pitch, yaw, tilt, etc. You can reset the "zero point" that is a baseline for the ECU when empty. If you don't do that - and you "level" your 4Runner, it thinks you have a few hundred lbs of cargo in the back all the time. Then the driver complains that the rear brakes were worn out in 30k miles. It's a result of the 4Runner thinking you're hauling a bunch 4-600lb of cargo all the time and using the rear brakes much more than it should be. It can also cause issues with VSC engagement and other safety features that rely on the pitch as an input to determining vehicle loading and predicting behavior.

This is how to do it:
Zero Point Calibration question