There is no such thing as a fixed front/rear ratio so in that sense 70/30 is bullshit. But they also put a rear disc on performance bikes for a reason. Until you are actually doing a stoppie, there is still rear braking power left. In normal street riding, people are not doing stoppies.
Personally I believe in approprite use of both brakes. My wife has a tendency to not use the rear brake and I have encouraged her to routinely use it. We ride a lot of dirt roads and contaminated hard surfaces and I don't want her to needlessly wash out the front trying to squeeze it harder to get the bike to stop in time, when she still has back brake capacity left unused.
The way to learn to not lock up the rear is to use the rear enough to get familiar with its characterisitcs, not to not touch it out of fear it will lock up. That's just as bad as the Hardly Dimwitson riders who supposedly are afraid to touch the front brake for fear they'll go over the bars.
Advanced pancreatic cancer found 04/2010. Have outlived +/- 97% of patients with this diagnosis, but 08/2013 cancer now in liver, vascular system and lungs with 20+ lung tumors. Sick/weak sometimes, not riding much. No more treatments & now under Hospice care.