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In the dynamics of braking, vehicle weight is transferred to the front, so the front tires have better traction. Having less traction, the rear tires slip more easily, and are more easily locked up.

Might be the same thing you are thinking of when you say the rear brakes are more efficient, but as far as the efficacy of braking a vehicle, the rear tires have less friction vs. the road than the fronts do.

There's a lot of difference in the weight transfer under hard braking on dry roads versus lighter brake applications on snow-covered roads. Brakes generally are biased towards the front because that's where the weight transfers during hard braking (just as you described). In the old days, a proportioning valve or dissimilar master cylinder sizes (for front and rear) made a specific bias to the front. It might be a compromise of sorts, but 75% of our driving is on good traction surfaces and that's where you want your best braking.

One of the phenomenon I experienced in the past - in the winter, it was common for us to add weight to the back of our 2WD pickup trucks for traction. Coupled with a limited slip differential and real snow tires, we got great traction in those trucks. But they became rear-heavy. On slick surfaces, it was easy to lock the front brakes while the rear wheels still rolled along. And with locked front brakes, of course, comes complete loss of steering control. It was not uncommon to hit the e-brake a bit to bring the rear tires into play when stopping.

Fun times. Of course, this was before anti-lock technology became common on anything outside of the most expensive sedans. There is a lot more at play in today's cars, thanks to technology. And it's for the better.