Having been using Minis in rallying since 1961 I've never found the pedals to be anything but ideal. The front to rear brake ratio can be adjusted with a valve at the rear and a servo is a personal choice. With regard to servos, I used to rally a 998 Cooper without a servo, but in all the 'S's I've had I have fitted the remote servo to reduce pedal pressure. That's a good thing on a long event. I did once try it without a servo and went out to test it on a night when the roads were wet. Going downhill into a tightening 90 right I braked, but the lack of pedal feel and higher pressure caused me to lock the fronts, then when I came off the brakes it over-steered and I just got round. I re-fitted the servo and it felt good again.
A friend of mine who also rallies a Cooper 'S' runs a later dual cylinder with no servo and says he likes the way the brakes feel, so it's personal choice. Best thing is to try them at competitive speeds and on slippery surfaces to see which is preferred and which gives best performance when times are compared.