They don't perform as well as other cars.
Race a Slash 4wd against a AE 4x4 or Durango desc410r.
Race the revo against a 1/8 truggy
Race a bandit against a 1/10 2wd buggy
Traxxas will always lose if both are driven by the same driver. I know someone who won a clubrace with a bandit and brushless set, but I guess that's because no one with skills showed up or they wrecked their cars