You're right. There can be big advantages to running different brands of motor in 13.5/GT12 classes.
I don't think that would apply to off-road at mendip though, simply because the nature of our difficult track means you're not relying on power. For example, I only ever run a Speed Passion 8.5t/10.5t at Mendip yet I'm a front runner against much quick motors.
Power is far from everything in off-road, I don't think there would be any need to regulate which brand of motor people used. The simpler the better
