Even if you assume the front brake provides the majority of braking power . . . (and I think 95% is a vast overstatement) . . . the rear still contributes additional power. If you want to stop/slow as quickly as possible and under control, using both brakes is the way to do that.

Lots of studies have been done for motorcycle racing where, for decades, racers bragged of using ONLY the front brake. Every study indicates that using both brakes is better -- and by a significant margin.