A lot of this is going to depend on "beat in what"? A BJJ guy is not likely to fair well in a TKD competition, and a TKD guy is not likely to fair well in a BJJ competition. There's an old saying that goes something like, "Don't judge a fish by its ability to climb a tree."
Some arts might fair better in one competition than the inverse. For example, a Muay Thai fighter I think will have an easier time in a TKD competition than a TKD fighter in a Muay Thai competition. But if you start talking about taking a full-contact MT guy and a competitive TKD guy and put them into a point sparring Muay Thai competition (like MDL), then they'll be a lot more even.