It was a pretty good deck at the time, you can't deny that. Different variants of it, including Landorus and Mewtwo mixes got tons of top cuts and a couple of wins. Right now I'm not sure if it can stand up to the speed of Darkrai, since they can hit the active for 110, then catcher the one with EXP Share and get a double KO, getting rid of all your energy on the board. I think Terrakion is meant to be a tech right now, and pretty much any deck that can tech it in without sacrificing too much concistency should definitely do so.
I don't understand why people fuss about how Terrakion techs ruin consistency. It's only 1-2 cards + energy, and it's fairly easy to find room for energy. Also, I think the tiny hit in consistency is well worth it, since the top 2 decks are both weak to Fighting. Also, being one of the few cards that can OHKO Darkrai EX warrants the space it takes up.
I don't understand why people fuss about how Terrakion techs ruin consistency. It's only 1-2 cards + energy, and it's fairly easy to find room for energy. Also, I think the tiny hit in consistency is well worth it, since the top 2 decks are both weak to Fighting. Also, being one of the few cards that can OHKO Darkrai EX warrants the space it takes up.