I can easily build you a system that will guess the price of a stock tomorrow wrong at least 90% of the time. Even 100% wrong if you'd like. How would you use that to make fewer errors in some other system?
For that reason error rates above 50% don't make any sense. Building a system, that is reliably wrong, is as hard as building one that is reliable correct, because the systems are the same, just with the output inverted.
The worst you can get with a system is 50%, at which point you can just flip a coin, because that is just pure random. Any deviation from that is going to be an improvement.