The XY OU Metagame is very interesting and I like it at lot because there are some stuff we didn't have in Gen 5 that help a lot. I'm thinking about Aegislash, Knock Off being stronger and helps a lot vs Stall, Mega Evolutions, Fairy Type helping against Fighting and Dragon type Pokemon, Assault Vest etc. You guys are wondering why Keldeo and Terrakion are so low in usage, and I personally think that this is a good think. Last Gen, there was no Team without Keldeo +/or Terrakion. Countering them was so difficult that we had to use Landorus-T + Lati@s almost everytime. As for their rarity in the tier, I don't really agree with this statement because people are now realizing / have realized that Keldeo is still extremely powerful and useful as much as Terrakion though I think Keldeo is a bit better in the current Metagame. The difference is that we now have other possibilities than counting on Lati@s/Landorus-T to handle them.
Weathers being nerfed is I think all we asked for this generation. Though at the end of BW2 people realized that Rain/Sun Teams weren't THAT much powerful, at least they know that Sand Teams are still the best. But now they all last max 8 turns with the appropriated item which actually totally destroyed Ninetales and Politoed. MegaCharizard Y has replaced Ninetales but what we called Sun Teams in the previous gen is gone. There is no more Dug + Venusaur + Espeon/Xatu/Spinner which definitely affects our teambuilding process. Instead of the handling a sun Team by using a Weather + X or Y Pokemon, we now have to deal with the weather inducer itself aka Mega Charizard Y that is to me one of the 5 best Mega Evolutions. It's now very interesting the way we now beat "sun teams" because we are no more afraid of Dugtrio which is a very important point because Dugtrio was probably the reason why Sun Teams looked so "broken" in Gen 5 and why Non-ScarfHeatran wasn't considered as a Sun counter. We still use Tyranitar to beat those Teams but this is the same problem as before: it isn't a reliable counter. While we had to be careful when sending in Tyranitar last generation, we now have to be careful with MegaCharizard's Focus Blast. There are also new stuff like MegaCharizard X, MegaGyarados etc to counter those Teams so that's why they are no longer used. As for Rain Teams, this is now purely offensive Teams because we can no longer use Rain Stall with Rain lasting max 8 turns (which means Politoed doesn't have Leftovers). Rain Teams are now improved Gen 4 Rain Dance Teams as there is a Rain inducer. But to close this paragraph about Weather Teams, Sun and Rain Teams are in my opinion dead. Weatherless and Sand Teams are dominating the Metagame and I don't think this will ever change. Sand Teams aren't affected because Sandstorm is not really considered as a "weather". There isn't Teams that take advantage of the Sandstorm like with Rain and Sun Teams. We use both Hippowdon and Tyranitar for a different purpose than setting up the Sandstorm.
Now let's talk a bit about the current Metagame and the most used Teams. Offensive Teams are currently dominating the Metagame though they aren't that offensive. I mean, with Defog, Assault Vest and the many bulky Pokemon we got, being offensive has a different meaning than previous generations. There's always something bulky in those offensive teams, I'm thinking about Aegislash, Conkeldurr, Landorus-T, Rotom-W, Mandibuzz, Zapdos, Mega-Venusaur, Chesnaught and the return of Suicune. With overpowered stuff like Mega-Pinsir, Mega-Lucario and Mega-Charizard X/Y, this is almost impossible to make a Team without using 1 or 2 defensive Pokemon. Knock Off, Assault Vest and especially Defog are the reasons of this new kind of offensive Teams in my opinion. Deo HO aren't that much used because of Defog and Genesect being able to OHKO Deoxys-D. I would like to talk a bit about Knock Off and Defog because those moves are the best things in this generation. The main point is probably the fact that they both are extremely useful against both Stall and Offensive Teams. An Offensive Team beating a Stall with no Stealth Rock up? Pretty much impossible. A Stall stalling without Leftovers? Pretty much impossible. Same goes for the Offense: no Life Orb / Choice Band. Stalling with no Hazards, this is quite a tough thing too.
This is why this Metagame is so interesting because it gives us more options to deal with any playstyles. There are so many things to try and many things actually playable and very good. I don't think I'm wrong when I say that we don't see the same Teams everywhere. With all the options we got and with Rain and Sun Teams gone, I think that the RMT forum will be full of great and original Teams. I still think a few stuff should get banned but this is without a doubt the funniest Metagame I've ever played after DPP.