The front brake is responsible for 70-80% of your stopping power, not to use them is foolish. If you only use your rear brake your developing very poor habbits. Should the need arise where you have to stop quickly (a car cuts you off, a dog runs out) your muscle memory skills are only going to go for what is used on a regular basis....the rear brake which is going to delay your abilty to stop by a huge margin.
Years back SportRider Magazine took a Bandit 600 (I think we all can agree it will stop faster then any big dog all things being equal, the laws of physics..a 450lbs bike vs a 700lbs bike and this is with out factoring in dual front disc vs single etc.
What the found stopping from 60 mph using just the front brake resulted in the following.
60-zero
front brake only 151 feet
rear brake only 289 feet
both front/rear 146 feet.