I have to be honest.
The only thing I have against SP is that everyone seems to be playing it and nothing else. Like everyone else has been saying, SP isn't everything, and as tough as a LuxChomp is, it doesn't auto-win all decks. Actually, it dosn't auto-win MOST decks. My Sunflora-style Jumpluff sweeps half the Luxchomp/dialgachomp at my league. Although that could be attributed to the fact that Genplume players are growing here as an anti SP.
Btw, Genplume ruled BRs where I live.
Also, about Gengar prime, I share Scizor' sentiments. I honestly don't see anything good about the card. Yes, it deprives setups by making your pokemon unusable. But otherwise, admit it, how many pokemon can your hand contain anyway? People will find a way of playing without leaving any pokemon in their hands, just as they can work around the current SF gengar, and even trainer locks. And Gengar's other attack is just meh. Besides, how many psychic energy would you want to attach to it, anyway? Think of the survivability rate.
IMO Machamp prime and especially magnezone prime will see far more play than gengar prime. Multiple Machamp primes with either nioqueen or blissey turns it into a tank, while magnezone prime is a claydol substitute with an excellent attack to boot, using upper and DCE. Hell, even a cubone tank might perform better.
On topic, IMO the most broken card is DCE. Yes, the humble energy card. I believe no LuxChomp player would disagree.