The exact opposite of that is true. If you use the FRONT brake all the weight is transferred to the front because the stopping point is at the front, so all the weight behind that is pushing forward still. Simple physics. That is the first thing you learn as a kid riding a bicycle, if you use your front brake only your weight will shift forward and you will go over the handle bars. Using the rear brake keeps the bike and rear end on the ground and is more stable than the front, not less. It's just that the front brake on a motorcycle has more stopping power (75%) so you should always use a combo of both brakes in an emergency stop.
You can still brake, to the point of cartwheeling a bike, while using both front and back brake. I rather surprised myself during a panic braking manoeuvre some years back, on the 410 south, when some moron swerved across three lanes in front of me while braking heavily, to make his exit. If anyone asks you, tell them that it IS possible to stoppie a VFR with linked brakes. My first and only rolling stoppie, and it happened at something just slightly north of 100 Kmh. I hope that I never do another.