Halcyon.
@Choice Specs
This post comes across as very biased in favor of Clefable, ignoring all of Tornadus-T's amazing qualities while highlighting all of Clefables and ignoring its own flaws. Clefable is certainly an amazing Pokemon, but I could just as easily say the rise in offensive Mega Scizor, Jirachi, SDef Taunt Skarm, and other Steels inhibits Clefable's ability to do its job just as easily as you can say Weavile's rise hurts Torn. Tornadus easily outlasts Weavile, with Rocks and LO wearing it down, its inability to switch into Torn, and U-Turn + Regen existing. The only fear it has is Pursuit, which can't even OHKO Torn after rocks anyway (252 Atk Life Orb Weavile Pursuit vs. 132 HP / 0 Def Tornadus-T: 198-234 (59.6 - 70.4%) -- guaranteed 2HKO). Susceptibility to status is not a good enough reason to keep something in S. Altaria is also susceptible to status unless running Heal Bell, but that takes a moveslot and an extra turn. Metagross is also useless if burned or paralyzed, bt it's still S rank. In fact, Clefable is the only S rank mon to ever not care about status moves, so I don't quite understand why that makes Torn-T not S material.Quite frankly I don't see Tornadus-T doing anything that sets it a tier above its A+ peers. I think that when used to its full potential, it is an incredible and malleable Pokémon that can do a lot for its team. However, in response to Halcyon. 's assertion of it being as good as Clefable, I just don't see it. There's just no using Clefable poorly: she can play multiple roles with just one set, has movepool out the ass, utilizes both viable abilities beautifully with no downsides/ways to combat them outside of Skill Swap, as well as sports great typing.
Tornadus-T is shoehorned into specific roles/tasks on a team with a variety of limiting factors, be it inaccurate moves, inability to run every coverage move, SR weakness, typing that leaves a bit to be desired both offensively and defensively, susceptibility to status (a paralyzed Torn-T is especially often dead weight), lack of physical bulk, susceptibility to priority, the rise of Weavile and spookiness of Pursuit in general, or lack of recovery without being forced out. When you specialize Torn-T to get around checks and counters or target specific threats, you tend to lose out on more than when Clefable does the same. When checks and counters try to cripple or remove Torn-T, they are generally much more successful than when they attempt to do the same to Clefable.
Torn-T really does shine in terms of splashability, and it's there to do it's job very effectively in much the same way that other A+ ranked mons do. Yes there are multiple sets to run that catch different mons, but generally Clefable is the kind of glue that Torn-T, strong as it is, cannot hope to match.
You say Flying is not an ideal typing offensively or defensively, but I disagree. Flying is notoriously difficult to switch into offensively, and LO Tornadus shows that. Defensively, Tornadus is a great defensive answer to Keldeo, Gengar, and Serperior while still maintaining offensive pressure, which cannot be said about other checks to these Pokemon (Mega Venu, for example, doesn't have as much offensive presence as Torn-T does, and also loses M=momentum when it is sent out, unlike Torn-T). Common flying resists are usually handled by Superpower or simply U-turned out of, with the added benefit of gaining back 33% health for doing so. You say Clefable doesn't lose out when trying to get around its checks, but when Clef doesn't run Flamethrower, it loses to Scizor and Ferro and other Steels. When it doesn't run Thunder Wave it becomes setup fodder/a free switch in for certain Pokemon. You say Pokemon can easily remove Tornadus-T, but Clefable can also be lured. SD garchomp only needs a LO to beat MG Clef. Thundurus only needs Nasty Plot or Taunt. Kyurem-B only needs Iron Head. Conkeldurr only needs Poison Jab. Manaphy only needs Rain Dance. Etc., etc..
Of course, everything I just said can be picked apart. You can tell me that these Pokemon's moves can be scouted for or that they're uncommon, or whatever. Bt the exact same thing can be said about Torn-T. Sure, Serperior can have Glare, but it needs to know when to use it, and even when it does, it still loses to AV Torn outside of extreme hax. And Clefable can still lose to a Latias if it turns out to be Mega Stored Power. You can say Keldeo can Scald Burn Torn (even though it still checks Keldeo when Burnt), but the same could be said for Altaria.
So taking all of the positive qualities for Clefable and matching the against the flaws of Tornadus is unfair. The positives for using Torn massively outweigh the negatives, so much so that it deserves S rank. It fits easily on teams, it covers a large portion of the metagame defensively while simultaneously being threatening itself, and provides utility to the team through Knock Off and Taunt, as well as momentum via U-turn. Would be counters such as Ttar, Heatran, and Skarm are either U-turned on, hit by a super-effective move, or have their items Knocked Off.