I disagree with any idea that involves Garchomp being less of a threat than it was in BW. XY gave Garchomp a direct buff(Mega Evo), some indirect nerfs (fairy types), and some potential metagame buffs (i'll explain in a bit)
Garchomp is still a monstrosity, one of the few Dragons that can plow through fairies better than the others can, while still being the powerful beast with coverage to back it up. First of all, Garchomp got a mega evolution that would be awesome or adequate depending on how XY is played. With a lot of items to run that benefit a slower paced way of playing, making most top tier meta pokemon relying on Bulky Offense (there was a thread about this). Garchomp fits perfectly into the Bulky Offense mode like it did in early/mid DPP and BW. If the metagame is slow enough, Mega Garchomp would be a premier threat, since its speed wouldn't be that big of a deal (same goes for Hydreigon actually, but fairy). Another thing to note is that the rise of fairies will make Mamoswine much less common, so Garchomp can go crazy.
The checks I expect to see to the Chomper are your typical stuff we saw in BW. Skarmory and Hippo are the main things, although hippo would be less common. XY checks to Chomp would be Talonflame and Fairy Togekiss, which do p well against it.
Movesets would also change a bit, with Rock Slide being potentially used more on SD sets (rather than say.. Fire Fang or Aqua Tail) along with Mega Garchomp luring abilities being used for some team concepts.
Overall, Garchomp is still a damn beast.