Ho-Oh should be eliminated; limited PP + recoil simply mean it will have no chance of making a 6-1 comeback.
Mewtwo should also be eliminated. If it decides to use Recover, it foregoes a coverage move. As devastating as it may be, Mewtwo simply won't be able to make a 6-1 comeback as well, mainly because everyone are so preapred nowadays (read: GENESECT).
Zekrom is slow. Sure, it has Roost now, but it's too slow and won't be able to take much damage. If it decides to go Scarf or CB it's too easy to play around it with 6 Pokemon.
I am honestly very iffy about Excadrill. What are the chances, that out of 6 Pokemon, the foe won't have Groudon, Kyogre, or Rayquaza? Very little. Therefore I say eliminate Excadrill.
Giratina-O just might pull off the sweep with SubCM/RestTalk CM. Dialga can terrorize the foe with its BU RestTalk set as it cannot be phazed, and Manaphy can easily stack up boosts and sweep the team, though I'm rather iffy about it as well, but for now it should move on.