I hate to be *that* guy, but I honestly think the PWT is an inferior Battle Dome in every aspect. The fact that most Gym Leaders are type specialists, with often one massive type weakness across their whole team, means move-spamming is usually the key to victory. They're too predictable: trainers with mixed teams would have been far better suited for the PWT, as in the Battle Dome. The consolation prize (a shard) is about as useful as the winning prize (BP), and it's rather disheartening to see people like it because it's good for BP-grinding.
White Treehollow/Black Tower on the other hand is a less derivative and more challenging experience, IMHO.