Interesting question Mike but I think the answer is no.
If it were just a case of friction, then the answer would be no. But tires on road surfaces do not operate on pure friction (the easiest proof that given a max. friction of 100%, then the best any vehicle could ever do would be to accelerate at 1g, and that would yield drag race elapsed times of ~10 seconds and we know that ain't right). Tires and road surfaces are both rough surfaces, with one digging into the other.
At any rate, the rear brake on any road vehicle does very little of the braking, at least when the brakes are used with some force. In fact, at some point in an 100% braking effort, assuming the brakes are powerful to lock the wheel (the case on all modern vehicles I think), then all downward force (what some are calling 'weight') is transferred to the front wheel(s) alone; this is what we see in a stoppie when the rear wheel lifts off the ground. The same thing happens at any application of any brakes on any vehicle but of course not so severely almost all the time.
I cannot speak for him but I think what Jim meant by the rear brake working so well on his cruiser is that it is much more responsive than the C-14's rear brake. And certainly I can believe that as the C-14's rear brake is pretty close to inert under any kind of moderate pedal pressure. So probably in normal, day- to- day, relatively relaxed riding, Jim's new bike has a more effective rear brake than the C-14 did, at least given the same, relatively light, pedal pressure. But speaking in global terms, all road vehicles rely on the front brakes to stop it as the braking becomes more aggressive and in any hard stopping, the front brakes will do the majority of the braking; if the front brakes failed on a vehicle (or were not used on a motorcycle that did not have linked brakes) then the rear tire(s) would lock and drag under no more than moderate braking.
BTW- this is the failure mode of tractor- trailers under extreme braking; the rear wheel- sets simply lock and drag without doing much to slow the vehicle down quickly. And if the tractor tires are doing the majority of the braking, the trailer would desperately like to 'whip around that decelerating place'.... this is what causes them to 'jackknife'.
Brian
Isn't it true to say that sometimes more weight (+where it is) can shorten braking distances (given everything else is identical) due to the improved mechanical grip on the road ?