Singlespeed with one brake...

single speed with rear brake = same stopping power as brakeless fixed

the most you can do on either bike, is lock the rear wheel up.

Both also carry similar risk for total failure of ability to brake, ie/ chain snap, or rear brake fail.

exactly

How the fuck is rear brake better than front??

Read Sheldon Brown on brakes.

you can turn and hard brake with rear brake more effectively than you can with hard front braking and turning.

but that doesn't mean its "better". front is "better" for stopping in a straight line.

you should have two brakes.