So I know you've posted around a bit with this question (mtbr and here), and I have the M9007 with this mount, and I have to say I don't really understand what the issue is. No matter whether the brake is on the seatstay or the chainstay, it's part of the sprung rear triangle, and it's going to affect suspension kinematics under braking equally. When I ride while braking in the rear I don't notice any differences in suspension activity or any lack of braking efficiency.
Since you brought up suspension, is the shock tune of the aftermarket Fox a great match for the frame's kinematics?
Did you request a firm XC tune?
Shock tune is based in the leverage ratio of the frame. There is some documentation from Rockshox in this:
check it out
