Definition of One Trick Pony

So my brain was wandering a while ago, when I hit this topic. Since we have the mastery functionality, we can now check if someone is a one-trick pony, vs someone who just has a main. I think the technique is this: Add up all the mastery of all their champs that aren't first, and see how that compares to their first mastery. If it's less than half, then that person is a one-trick pony, and banning that champ will probably mess them up horribly. What do you guys think?