With enough brushless motors to pick from these days, the guys who already have the equipment wont want to spend x amount on old technology and keep rebrushing/ it.
Keep stock for the newbie, 13.5 for the middle class as it has more torque, or even 10.5/19t if the track allows, and outlaw/mod any motor for the pro.
tbh though, it really depends on the size/layout of the track and the number of people racing to detemine which classes best suit the venue. It can be a tough call sometimes what to do for the best, but if it isnt broke dont fix it....
