Here is my line of thinking based off of what you're saying:
[Link to serebii with all Sand Veil users: http://www.serebii.net/abilitydex/sandveil.shtml]
[Link to serebii with all Snow Cloak users http://www.serebii.net/abilitydex/snowcloak.shtml]
Garchomp, Sandslah, and Cacturne (excluding NFE's) all have sand veil as their only non-DW ability in 5th gen. In sand, these pokes would be be violating the heart of the Evasion Clause, not the letter. If we are going to look at Garchomp and ban it because of its sand veil ability, what of Sandslash and Cacturne? While I agree their respective movepool, base stats, and typing would make them inferior to Garchomp, we cannot ban Garchomp on grounds of the Evasion Clause with its Sand Veil ability if we do not also ban Sandslash and Cacturne respectively.
For Snow Cloak, Glaceon, Froslass, and Tsunbear all have only Snow Cloak as their ability, again non-DW. If the community decides to ban the Snow Cloak ability for violation of the Evasion Clause, then the community is also effectively banning Glaceon, Froslass, and Tsunbear because they lack secondary abilities.
If the community were to decided to ban just the Sand Veil / SnowCloak ability because of the Evasion Clause, then that is the same thing as banning Garchomp, Sandslash, Cacturne, Glaceon, Froslass, and Tsunbear, bar DW abilities, because they lack secondary abilities.
However, the community may decide to change the nature of the evasion clause for the 5th gen, or add/subtract to/from it. In this case, my argument may be in vain.
The big question, is an evasion-boosting ability broken enough that the community decides to ban it or not? Does the fact that these abilities require weather affect the effectiveness of these abilities? Will we see a upsurging of Cloud Nine bearers (Golduck or Altaria/Likcylicky in DW) in order to counter the potential threat from evasion-boosting weather mons?
If Garchomp gets re-classified as ubers and not Sandslash, Cacturne, Glaceon, Froslass, and Tsunbear, then it is not because of his ability to dodge opponents attacks in the sand, it is something much more.
He's not saying that they are broken, just like evasion may not necesarily be broken. they are simply haxy beyond what the community is willing to tolerate. Last gen we had to, since they had no alternative abilities. Now they do, and we can ban the abilties without banning the pokemon.