i'm not saying it's good in its current itteration, but focusing and not making mistakes doesn't make it bad, seems like a weak argument to me. Scaling up doesn't make it a better experience either, so i don't quite get your thoughts!
The endless waves etc are kind of cool but there doesn't seem like there is much guidance in the proving grounds. i want it to be a system of learning about the game, learning about your class and learning how to improve. I hope that blizzard continues to enhance the PG!