I think there is a misunderstanding of high regen regarding efficiency. High regen for a stop in which the disk brakes are not used is definitely less efficient than low regen. The only times high regen is more efficient is when you want to stop so quickly that on low regen the disk brakes would have to engage.
Higher regen in efficiency terms has the same effect as stomping on the accelerator except the current is in the opposite direction, higher currents causing greater resistive losses, greater torques, greater loads, greater friction, all heat generators. In no case does regeneration cause these losses to become gains.
The highest efficiency would be like hyper-milers do in 1st generation EVs where they accelerate slowly and try to coast to a stop which pisses off everyone behind them off.
A true 'no compromise' system would be closer to my 2014 Chevy Spark that modulates the regen with the brake pedal until you press too far and it then starts mixing in disk brakes.