This, I think, is the (potential) value of martial arts training for a kid who's being bullied: not because it will teach them fighting skills to defeat the bully, but because it puts them, for a short time at least, in an environment where other kids treat them with respect and care. It's a sanity check that says, "It doesn't have to be like that."
Too, I think taking a martial art teaches kids to carry themselves in such a way that they are not obvious targets. When my son was in kindergarten, all the mothers were calling around about one child who was bullying most of the boys. I had heard nothing about it. When I asked my son, he said, "He doesn't bother me. I take aikido."