Tornadus-T has 3 attributes going for it - Regenerator, STAB Hurricane, and 121 base Speed.
Regenerator is cool until you realize that the awesome 33% recovery is stunted by its SR weakness and LO recoil. You wont see Tornadus-T magically healing itself upon switching out the way Tangrowth and Slobro might. Regenerator is a major boon for a SR-weak mon, but in a similar vein its restorative powers are restricted by SR weakness and LO recoil - bringing down Tornadus-T is not a difficult feat. Tornadus-T is essentially coming into the field with 75% health or less. It's much like Dragonite or Volcarona; get the rocks up fast and their infamous durability goes down a notch or more.
STAB Hurricane is certainly powerful, but we're prepared for them. We had to be prepared for Hurricanes since the inception of BW, otherwise our teams would easily be decimated by Tornadus-I's Hurricane coming from a 125 base SpA. If we can tank Hurricanes from Incarnate, and we can very damn well take the notably weaker Hurricanes from its Therian forme.
So the first two attributes do not ascribe to the suspect status of Tornadus-T, as explained above. What about its base 121 Speed? Now this is where some justification lies. During BW1, the Incarnate forme was easily checked by Starmie, Alakazam, Scarf Tar, and even Dugtrio! However these predators now become prey to the faster Tornadus-T. Truly, base 121 Speed breaks the Speed tier of OU?!
Not quite. Yes, base 121 Speed is a large advantage of Tornadus-T that has given it the upper edge against many OU threats. However, we're prepared for much faster and dangerous threats, such as Chlorophyll Venusaur, Scarf Mence, Scarf KELDEO, RP Landorus, SubSalac Terrakion, and even DDNite. Your team must have Pokemon to deal with such threats that would exceed Tornadus-T's Speed, so checking Tornadus-T with a Scarfer, stronger priority, or through counters should not be a foreign concept for competent players.
Tornadus-T is simply a faster and hardier and less powerful Tornadus, a Pokemon that has now been residing in UU for quite some time now. OU is perfectly adapted for Tornadus-T, imo. Prevalent OU mons like Rotom-W and Jirachi hard walls it, and there's no shortage in checks in the forms of faster Pokemon, strong priority not named Mach Punch, and Pokemon bulky enough to survive a Hurricane / Superpower (ie Heatran, Ferrothorn, Kyurem-B, Politoed, Garchomp lol etc).
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I've read some people likening Tornadus-T to the recently banned Genesect. Tornadus-T and Genesect are both powerful threats with a fast U-turn.
The similarity ends there.
Genesect has more going for it. It is not a one-trick pony like Tornadus-T. You see a Tornadus-T and you pretty much know that you'll be dealing with a special offense threat capped at 375 base Speed. However you never know with clear certainty of the identity of Genesect. It may be the more common Scarfer with 440+ Speed that plagues slower dragons and Psychic-types - or it may be an offensive EB pivot that is capped at 326 Speed but can switch moves and gain surprise kills. Even more, Genesect may be the devastating Rock Polish Sweeper that can sweep in a moment's notice once that one Genesect counter is removed.
Genesect is much harder to pin down than Tornadus-T, being only nominally vulnerable to SR, resilient to most priority moves, and possessing the amazing resistances of Steel-types. Genesect has far fewer checks and counters, unlike Tornadus-T, and those few checks and counters are much easily disposed of than those of the Therian.
Not to mention Genesect's U-turn actually HURTS, given its 120 base Attack plus STAB and possibly a Download Attack boost. This pales in comparison to Tornadus-T's puny non-STAB U-turn coming off from a 100 base Atk - a pittance indeed. You can afford to spam U-turn with Genesect and be rest assured that you're wearing down the opponent fast, but the same thing cannot be said about Tornadus-T, who will be taking LO recoil as it U-turns out, and heavy SR damage as it comes back in. If the Tornadus-T player uses U-turn only for the opponent to keep his Pokemon (say a Terrakion) in, Tornadus-T player will be left in an awkward position. If the opponent finishes off a Terrakion (which would survive a Hurricane / Superpower at full-health lol), then the opponent can simply bring in their Tornadus-T's check / counter and force Torn-T player in the defensive. Nothing here screams Torn-T player having a drastic advantage over the opponent. Tornadus-T cannot afford to brainlessly spam U-turn / Hurricane the way Genesect can spam U-turn and get away with it.
Not to mention Genesect works in ANY PLAYSTYLE, be it Rain, Sun, Sand, or weatherless. No matter how dominant Rain is in the current meta, Tornadus-T will never be as omnipotently useful as Genesect.
Let's stop treating Tornadus-T like Genesect, and treat it more as a slightly better Tornadus-I, because that's a much more accurate representation of this Pokemon.
In the end, Tornadus-T is not an Uber - its Speed, STAB Hurricane, Regenerator, and U-turn are attributes that are perfectly manageable in OU. RP Landorus, Terrakion, the copious number of dragons, Thundurus-T, and Keldeo are much more threatening threats than Tornadus-T.