If you're locking the rear wheel, that means your brakes (or you) are increasing the pressure too suddenly, kinda like it's all on or all off.
My discs remain pretty linear no matter how fast I grab my brakes. I mean I can lock them but it's harder to lock my discs than my regular caliper brakes and I can better control how I decelerate with them.
Technically you can just get rid of your brakes and go fixed.