Just stopping by to point out that, while I acknowledge that a lot of them might not be especially viable, there are ways to counteract Sand Veil and, though I acknowledge that Sand Veil will usually be in force under Sand, saying otherwise is simply not true. For instance, Mold Breaker and No Guard block it, while Compoundeyes cancels it out. Now I acknowledge that the only viable mon with any of those abilities is Haxorus, who can only outspeed with Choice Scarf (and only non-scarf Garchomp at that), and, of the rest, only Golurk, Machamp, and Galvantula are anywher near usable, but the fact remains that there are passive ways to remove Garchomp's passive hax without changing the weather.
Outside of abilities like these (to which Mummy could also be possibly added in as a temporary, only sometimes helpful measure), there are also several moves that avoid or neutralize Garchomp's hax outside of the already much maligned infinite accuracy attacks. Namely:
Ghost-type Curse
Destiny Bond
Defog (though blocked by sub and generally counterproductive)
Coil
Gravity
Hone Claws
Lock-on (though blocked by sub)
Mind Reader (though blocked by sub)
Perish Song
Skill Swap
Sweet Scent (though blocked by sub)
Telekinesis (though blocked by sub)
Yawn (though blocked by sub)
As for items, there's really only Zoom Lens on slower things, but it is an option and would mean you'd never have to worry about shit like Skarmory Whirlwinds missing (and hey I've seen people run things like Rocky Helmet on Amoonguss in NU to beat Cinccino, so running an item over Leftovers to beat a specific Pokemon isn't entirely unheard of).
Now, let me be perfectly clear: I am not, not, not, not, not saying that any individual one of these moves, abilities, or items (really item) are viable options. I'm not even saying that any of them are. However, the fact is that there are ways to get around Sand Veil hax outside of running incredibly low power or poorly distributed moves. Are they usable ways? As I said earlier, I'm not sure (and some, like Sweet Scent and Defog, I'm near positive aren't). But the fact remains they're out there, and some of them might be worthy of consideration.
Edit: This is also not an argument either way vis a vis Banning Garchomp, Banning Sand Veil, or Banning anything else. It's just something I wanted to bring up.