Sand will almost surely be broken without Sun and Rain. Stoutland, Sandslash, Terrakion and Sand Force Landorus will all make sure of that. Good luck building an offensive team with Sandslash and Stoutland lurking in the corner, which will be able to revenge kill almost every offensive threat, and quite easily sweep. Oh and Terrakion... This beast will have a 324 SpD stat coupled with a 324 HP stat, which means that he will be able to set-up on most special attackers in OU, and then decimate your whole team after an SD / RP / Sub. An argument could also be made that Hail alone would become broken, if it was the sole perma-weather. As UU has shown, we should not underastimate the power of sole perma-weather, even Hail's. You haven't faced the nightmare called Snow Cloak Froslass under constant, unremovable Hail. Or Snow Cloak Mamo. Or Specs Kyurem spamming Blizzard. You though SubKyurem was annoying to deal with if T-Spikes were on the field? Then add Hail damage to the mix, and a more pwoerful STAB on his hands, and sweet dreams.