Autobrake settings are pre-programmed decelerations rates indeed.So,when using long rwys,and braking 1,with reverse idle or more,almost NO braking is applied on wheels,the deceleration rate is reached with reversers only.
You can check this also,by monitoring brake temp in such a case.Of course,as speeds decrease the efficiency of reversers decrease also,so much braking force applies on wheels.
You may try this by selecting no autobrake,deploying reversers and monitoring deceleration rate.It will be enaugh on a long ,dry rwy.From around 80kts you should apply brakes also,due to reversers efficiency.