Actually, Double team is banned because it makes the game even MORE luck based then it already is, which is not very conducive to a Competitive environment. Also, the Double Team ban is more of a Courtesy used by a lot of players, many who ignore smogon still follow it.
I do agree on the drizzle/swift swim part though, it is stupid and seems there just so their precious Sand teams are kept the most powerful. They also are a bit hypocritical with their Ban list, banning some pokemon deemed powerful but ignoring the ones used on nearly every team and who shape the meta game. Still they are the only source outside of the official one to try and help with the games balance, even if they are not always very good at it, you have to give them that at least.
Anyway, YAY, Xerneas's stats are revealed, now for someone to figure out what its base stats are