No, the weight-shift is caused by deceleration-G, doesn't matter if it's the front or rear brake that's doing it. Just that the rear can only do so much deceleration before the weight is lifted enough for it to slide. The front can do a lot more deceleration before sliding.

By letting off the front-brake when the rear slides, you are decreasing the deceleration-rate, reducing the weight-transfer to the front and add some back to the rear. That will lengthen your stopping distance due to the lower deceleration-rate, not what you want if you're trying to stop quickly. The idea then is to put your belly on the seat with your 'nads skimming the back tyre and add more braking-force to the front. This will increase deceleration-rate and stop you faster than trying to let up on the front and using the back more.

Just try it, practice stopping in the shortest distances possible in a straight line. You'll find that the fastest deceleration is when you can get as much grip on the front as possible just before it slides or before it flips you over the bars. Doesn't matter what you try to do with the back since it's only 1% or less of the total braking-force at maximum deceleration-G.

Now, braking while cornering is a completely different matter.