Rain teams and sandstorm teams are definitely dominant in this metagame, even with the inclusion of Blaziken. Manaphy, Keldeo, Thundurus, Tornadus, and Dragonite are just a few of the excellent rain abusers in the tier, and it is relatively simple to make a team built around one or more of them. Since Deoxys-S is also allowed in the tier, offensively oriented teams are even easier to pull off, and are usually successful.
What I'm really loving in this tier is Volt Absorb Raikou. Similar to UU, SubCM Raikou is an excellent sweeper if provided with spikes support. Volt Absorb just gives it even more opportunities to set up, as it is now immune to Electric-type moves, including the previously crippling Thunder Wave. It can easily abuse a powerful STAB Thunder with rain support, and provides an important Electric-type immunity for rain teams. Everyone seems to think that rain is all about Thundurus/Manaphy/Keldeo, but less-used Pokemon such as Raikou and Tornadus can easily take rain teams by storm, literally.
As for the topic regarding Excadrill, I'm really glad it's been given another chance at OU in the Dream World metagame. With things such as Technician Breloom and Air Balloon Blaziken to check it, Excadrill is a much lesser threat than it was in BW OU. Granted, Excadrill is still amazingly good; I mean, who can resist that sexy base 135 Attack, or that doubled Speed in sandstorm that even Deoxys-S can't outrun? There's numerous different ways to deal with Excadrill, and a lot of them haven't been discovered yet, or aren't very well known. For example, if my Politoed has perished already, and the opponent still has sandstorm + Excadrill, I have one last-ditch move in order to save the game. The key is Tornadus. Tornadus, unlike Thundurus, has access to a priority Tailwind. While this may seem gimmicky at first, I really only use it as a last-ditch attempt to save myself from being swept by Excadrill. Since Tornadus will always go first thanks to Prankster, my team will receive the Tailwind boost while Tornadus sacrifices itself to Excadrill's attacks. After that, I will bring in a Pokemon with a higher base Speed than Excadrill, such as Garchomp or Keldeo, and proceed to smash their Excadrill with Earthquake or Hydro Pump, respectively, thanks to the doubled Speed provided by Tailwind. It is strategies like these that makes the Dream World metagame so enticing; there are endless possibilities to what you can do, there are just so many great options and opportunities for a person to be creative when making a team.
I personally think rain is much more versatile and fun to use than sandstorm, as all sandstorm really can do effectively is just abuse Excadrill, Landorus, etc. Rain just has so many more possibilities, and that, in a way, makes it a lot more dangerous than sand. Of course, there aren't any Swift Swimmers thanks to the ban, but it still poses a remarkable threat with all the aforementioned characteristics.
However, despite the fact that I think this tier metagame is relatively balanced, I do agree that Blaziken is a major pain in the ass to deal with. Speed Boost is an incredibly ability, and now combine that with the fact that Blaziken can utilize Baton Pass in the Dream World, and you have one crazy good blazin' chicken on your hands. Although the Dream World metagame is relatively new, and I would still probably wait a little while for people to adjust to the metagame before putting anything up as a suspect, Blaziken is definitely the first Pokemon that comes to mind as a suspect.
