It seems to me that having people do extended time in GA etc has one main effect....it allows the pilot to know what scared is and hopeful he becomes a more aware pilot because of this.
Studies seem to show that low hour cadets when tested fit within the range of acceptible standard though probably at the lower end. A bad pilot is still an unsafe pilot whether he has 20000 hours. A supervised SO with low hours is probably still safer.\ than him.