Hi there - I agree with you in regard to the braking, useless and difficult at best. I say this largely as I am having great difficulty if settling on a new working button configuration for the controller.
All the way through the GT game series I have used the R1 & R2 buttons for braking/acceleration and the L1 & L2 buttons for gear up/gear down. I was mortified to see that we are unable to reconfigure the R2 & L2 buttons with the stock configuration and have been unable to work out a suitable alternative configuration with all the options of buttons, sticks etc.
Despite hours of practicing and hundreds of laps, on even the most basic track, I am unable to do laps without reverting to style and either accelerating when I should be braking, looking backwards when I should be changing gear and , as for braking whilst changing down and steering around a corner whilst looking behind, forget it!
Maybe my advancing years have slowed my reflexes some, but I am unable to go back to playing GT6, and my old configuration, whilst I am trying to get to grips with a new button combination.
Please bring back full reconfiguration of ALL buttons.
Cheers