Back in February, I did some math to study accuracy vs. power in the break shot. My findings were interesting, but not too surprising.
The basic conclusion is this: If you hit your break shot with only 1% of error (i.e., 1% off from a dead-perfect hit) you lose 1.57% energy. So accuracy is about 1-and-a-half times more important than power, when it comes to energy transfer.
So your point is valid, but we are humans and not calculators, so let me tell you why power is (for most of us) still very important.
Let's say you are breaking at 20MPH and you are able to get to 21MPH, that's a 5% increase in energy sent toward the rack.