As far as brakes being overpowered...
In my experience with discs, a decent set(Mine have been Avid mech and Deore hydraulic) the actual skid power is lower than that of V-brakes. Sure skidding is possible but it is a conscious effort, not an accident. That makes me feel more confident in the braking ability/control on the mtb under high speed situations, wet or snow etc especially on the road.