Something to remember about weather is that, while very few Pokémon get Speed/Attack boosting abilities for Sandstream (lol Dory and Landlos, nobody cares about Sandlslash), those two are generally way better than most stuff useable under rain.
Things such as Ludicolo and Gorebyss have no boosting moves, subpar special attack (Ludi's is only 90, Gorebyss is still way lower than Dory's attack) and maybe even somewhat bad speed. Even stuff like Kabutops, which can boost it's attack, has an enourmous ammount of flaws. Only Kingdra is actually good independent of weather.
So, what's the point? Even if Sandstream gets very few abusers, those are actually some damn good ones, way better than the stuff rain has. I guess that's something to keep in mind when discussing the impact weather has on the metagame.
I left Manaphy out on purpose because I'm quite sure noone disagrees that it's a broken bitch under rain. i.e: if we assume Drizzle stays in OU, Manaphy surely is leaving.
Uh...Gorebyss has Shell Smash and Ludicolo can Swords Dance. And 90 special attack is useable. Like, Life Orb Focus Blast 2 hit koes max hp/max SDef Nattorie, has stabbed Giga Drain/Surf, has Swift Swim, etc. And if Gorebyss gets Shell Smash short of Nattorei/Blissey, the thing will pound you to pieces and both Nattorei and Blissey are easily 2 hit koed (and even if Nattorei kills it, it would be so weakened that any other Swift Swimmer can kill it). Kabutops does beat Nattorei if Nattorei switches in and not many use Erufuun. And Roopushin needs Guts for Mach Punch to ohko Kabutops (after Life Orb), Hitmontop has almost 50% ohko after Life Orb (and still not many use it), Breloom is the only one ohkoing.
The thing is, in rain although they are average to useless outside it, is that in rain, they are phenomenal. Sand has useable users outside of Sand (Garchomp, Gliscor, Landlos). And unless you change the weather, rain is going to go on. The problem is, how you're going to switch your weather user in since Sand and Fire teams are weak to a lot of the moves water users would carry. Politoad can 2 hit ko Tyranitar in Sand (ohko with Specs Focus Blast if it doesn't have Special defense investment). Tyranitar/Hippowdon/Ninetail can't really switch in on anything and really only Abomasnow can on certain things (not Focus Blast, Rock Moves, Fighting moves, etc) and few use that.
What are you talking about? Gorebyss's special attack is only 10 points shorter than Jolly. And has double stabbed Swift Swim Surf/Hdydro Pump, the potential to use Shell Smash and be unstoppable in rain (808 speed), etc. And while it is meh speed without rain, after Shell Smash it still outruns non-Scarf things and Choice Scarfers of <86 speed that aren't running positive speed natures. No weakness to Mach Punch at least and only Breloom comes close to ohkoing with Mach Punch after -1 (but even with one round Life Orb it has 66.67% of surving).
Manaphy would be broken even without Drizzle (can set up it's own Rain Dance which means Water absorbers will wall it but wouldn't really do anything back and dragons resist although if facing a +3 Tail Glow, will be 2 hit koed)