SP has been one of those mechanics that started out fine. When it was born in Platinum, I myself liked the idea behind it quite a bit. Basics that were actually really good, and had their own engine. They brought to the table a fair amount of skill given when they were introduced. Power Spray was one of those cards that one really had to decide when they wanted to use during that time, and Double Colorless was no where to be seen. SP's had a lot of great cards when first introduced, Dialga G and Palkia G being the biggest ones, and soon to follow was Luxray GL. Still, during this time, everything was balanced. SP's had a great addition, SP Radar, but, they still had opposition in the forms of Flygon, and Machamp. Beedrill could even take them to a degree, as was seen by Raybees. Gyarados soon hit the tournament scene, and still, things were balanced between the world of SP and Non-SP. But, when DCE hit the field, that's when the problems occurred.
When DCE was released, that let LuxChomp off the leash, and allowed it to rise above the other SP decks and become the biggest problem.
What's made things worse is that LuxChomp has only gotten more and more things to use. Entei Raikou Legend, Junk Arm, Communication, and Twins were the biggest things. This one deck has gotten so much support, and when Claydol left the format, other decks got hit hard from the loss of their biggest engine. Sure, Uxie was still there, but, that was the problem. It was ONLY Uxie to give these other decks draw power. Being able to stop an Uxie meant that SP's could just pile drive decks into the ground because they could not get off the ground - the exception to this, as of right now, being Vileplume variants. Further, since LuxChomp has had so much in its court, everything else has to work to be able to fight back against the deck. Even worse is that its speed has been hard to match with most decks; speed has been too big of a deciding factor for these past two formats. It's ridiculous when speed alone has to decide an entire format. Formats should not be about who's as fast as The Flash. (Hidden Legends on was a prime example of what a format SHOULD be. There were multiple decks, not just one big beefy deck that shut out all but two other options, and speed wasn't such a large factor. It was clearly a good thing, but it did not absolutely decide everything. LBS was a great deck, yes, it had a lot of speed and power, but the other decks in the format, such as Pow!Tar, Flariados, MewTric, Rock Lock even, were available. This format was completely balanced, and skill was the deciding factor most of the time. Not that it isn't now, but that'll be addressed later). If it wasn't for things like Broken-Time Space, Evolution decks, in my honest opinion, would not stand a chance. One card versus an entire engine given to an entirely basic deck that is up and going constantly by turn two. Gyarados is an incredibly fast deck, clearly. It has the potential to disrupt powers like LuxChomp does via Mesprit. It has an attack that does ninety for no energy, and 110 with Expert Belt. But, it has to play cards specifically aimed to getting the chance to be able to disrupt powers, it has to play a lot of trainers just to get off the ground as fast as it does. What does LuxChomp have to do? Play the engine that was handed to it from the start that allows it to both set up and disrupt powers, and has an easy time of getting their important cards back to hand to use again. On top of that? It has a multitude of counters that can be tech'ed for whatever match-up might prove difficult.
I know that I simply cannot stand LuxChomp at the moment. I know that it does take some skill backing it for match-ups like mirrors, or other SP variants. However, it's ridiculous when seeing someone run hot with LuxChomp. It's hard to beat someone that's running incredibly well if they have LuxChomp in their hands. And, if your starting hand is awful to begin with, your chances of winning are fairly low, depending on the deck that you happen to be using. If it's another SP variant, and your hand is awful, you're done. If it's Gyarados, and your hand is awful, you're done. Vilegar is about the only deck that I've seen that can cope with a bad hand, but even it has its own issues.
I really don't hate all SP's. LuxChomp is just the one deck that I cannot get behind. It's incredibly boring. I'm not a fan of a deck that pretty much had everything handed to it. But, while it was incredible last format, and has proven to be good in this format, as Ignatious pointed out, it's also heavily played. That's a huge factor in why it wins as much as it does (even though it has a ton of different counters for certain match-ups). Things like Gyarados and Vilegar both can contend with it, and contend with it well. But, in the end, It comes down to speed or trainer lock. And with speed comes a lot of luck. Incredibly boring if you ask me.