Again, spore can be negated by Herbivore and Dark Void doesn't have immunes. Therefore you can't say it is strictly better if we can't argue the same for light ball because it simply isn't the case. Sure the 20% accuracy is far better and less situational, but what Latios would want +1 spa/sdef when he could have +2 spa/att? If Pikachu can go physical with 55 attack Latios can do it with 90, on top of an automatic Nasty Plot from base 130 SpA. The difference is in the users, like Dark Void vs Spore.
If drizzle is banned we should put Kyogre in OU just because we can... XD
Except for the fact you simply couldn't do that unless we allow no ability Pokemon which is another issue. Things like Drizzle/Sandstream etc can be discussed being banned because they're powerful but that the Pokemon have alternative abilities which while not nearly as great make it so they aren't autobanned by default. I don't know if Kyogre without Drizzle would be OU or not (it potentially might be, but then looking at it's still disgusting stats all round and really good surviveability it seems unlikely even if Kyogre could somehow exist without Drizzle) but it wouldn't matter.
Soul Dew is the broken item because of it's users which was a free +1/+1 with NO downsides that are FAR better than the other item users. I mean, things like Clampearl, Marowak, Pikachu, etc wouldn't be seen because they (except Pikachu who is unfortunately outsped by a lot of things in OU who murder him) are SLOW and have crappy defenses (at least on some side), no recovery, etc. Unlike Latias/Latios, they'd need additional things to even remotely be viable while Latis are viable with or without. With, they have uber stats and Recover. Without, they still have impressive stats and speed. 110 is insanely fast for most things and they have decent enough physical defenses and special defenses that make them going down in one hit very hard since you'll have to outspeed them or survive (and taking Latios's Draco Meteors as everyone knows hit like a truck on nearly everything). Latios (at least) seems broken without Soul Dew. Latias maybe not so much but it definitely overcentralizes.
Darkrai is probably too powerful with or without Dark Void (like Latios without Soul Dew although Darkrai could only wish his stab moves were as strong). And he's faster and carries Nasty Plot which is instant +2. Admittedly without Dark Void, it will force Darkrai to carry something to further extend it's coverage which could potentially make counters worse like carrying Psychic to destroy fighters, Substitute for protection, Taunt to stop things from trying to mess with it, some sort of other coverage move (Icebeam/Spacial Rend/Thunderbolt), Trick to screw people over with a Choice item it doesn't need anymore, etc. It could run a Specs set as has been suggested which will hurt extremely hard as well. It could also potentially run a mixed set (90 Atk isn't bad and it has Swords Dance and Stabbed SUCKER PUNCH). Darkrai would be slightly harder to set up and there is no longer the fear of your Darkrai counter potentially being Dark Voided and essentially Death Sentenced so there is no longer the almost need to let it get free boosts, but it could still be extremely damaging and for OU, it has quite respectable defenses (after all, it is only 2 hit koed by Scizor Punches and the only Mach Punches that ko are Breloom, Hitmontop, and maybe Guts boosted Roopushin although if it carries Chople it would live all of those easy). Darkrai has enough power to still potentially be broken even without Dark Void.
And if one is implying Dark Void is broken, it also logically follows Darkrai is broken (let's be honest, he's the only one who uses the move). Because he is the only user, if Dark Void is broken but not Spore, it has to be because Darkrai is broken, not Dark Void because Parasect/Breloom/others aren't broken with Spore. Spore is the better move obviously yet Dark Void is the one complained about...running off of Darkrai's 125 speed stat.
