Riding at WSB and Mtg levels is not possible on the the street, but being able to brake leaned over is important.
I read that a Mtg rider will enter the corner hard on the front brakes, flick it to his knee, adjust throttle(for available traction), use the rear brake to controll wheel spin, weight the footpegs(Raine was said to wear out a pair boots in a race), push the bike up with your knee(Diahann said he did that 2 or 4 times a lap), ease off the brakes, use the front brake to give the front tire some traction, and then square off the turn. The rider is also thinking on how to pass the rider ahead and deal with tires that are going off. I don't wonder why they are paid big money.
Sorry,I got off topic, I do brake into the corner, and I try to most of the braking straight up, but that is not always possible. When I ride the twisters, I tell my friends I do not use brakes, just engine braking. For me its a fun way to judge corner speed.
Steve