I don't think Torn T is broken, he's everywhere (and he should be) but he's not 2hkoing things like Weavile did or walling half the metagame like Chansey was. People say OMG REGENERATOR, but he's weak to rocks. Essentially all that chip damage you land on him is permanent when rocks are on the field. He also can't break walls without life orb, which hurts his survivability even more. Then you realize his best STAB is 70% accurate. Itemless physical sets work but are walled by any bulky water or tank not named Chesnaught, and therefore not hard to find a switch in for.
I feel like he's going to stay banned just because people are already in that mindset that he's broken, but as a neutral observer with 0 emotional investment either way, I think he should stay.
But, that's the problem with Torn-T. You don't know what set it is running. Let me show you some calcs. Let's say you see Torn-T and assume "Hey, it must be the itemless Torn-T. You send out Slowbro, knowing the best that he can do is Knock Off (and if you have Rocky Helmet, that's even better!). You run your calcs and they look:
252 Atk Tornadus-T Knock Off (97.5 BP) vs. 252 HP / 252+ Def Slowbro: 120-142 (30.4 - 36%) -- guaranteed 4HKO after Leftovers recovery
And then Torn-T hits Slowbro with Grass Knot...
252 SpA Life Orb Tornadus-T Grass Knot (80 BP) vs. 252 HP / 0 SpD Slowbro: 244-289 (61.9 - 73.3%) -- guaranteed 2HKO after Leftovers recovery
So, going purely physical is a bad idea, what about going special and lots of HP, good ol' Blissey!
252 Atk Tornadus-T Acrobatics (110 BP) vs. 252 HP / 252+ Def Blissey: 271-321 (37.9 - 44.9%) -- guaranteed 3HKO after Leftovers recovery
252 Atk Tornadus-T Superpower vs. 252 HP / 252+ Def Blissey: 396-466 (55.4 - 65.2%) -- guaranteed 2HKO after Leftovers recovery
Whoops, Blissey is gone after SR and switching into Acrobatics (easily a spammable move).
Mega Aggron can tank hits left and right and doesn't care about some SE non-STAB fighting move...
252 SpA Life Orb Tornadus-T Heat Wave vs. 252 HP / 4 SpD Filter Mega Aggron: 216-255 (62.7 - 74.1%) -- guaranteed 2HKO
Whoops, Aggron is 2HKO as well. Surely, Florges can save us!
252 Atk Tornadus-T Acrobatics (110 BP) vs. 252 HP / 236 Def Florges: 153-181 (42.5 - 50.2%) -- 41.8% chance to 2HKO after Stealth Rock and Leftovers recovery
252 Atk Tornadus-T Acrobatics (110 BP) vs. 252 HP / 0 Def Florges: 205-243 (56.9 - 67.5%) -- guaranteed 2HKO after Stealth Rock and Leftovers recovery
You can't assume Torn-T runs one set. It gets phenomenal coverage;
even more so than Victini, but it has greater Sp Atk and Speed, similar bulk, less weaknesses and can Regenerate it's health back. It can pick and choose it's coverage moves to take out it's so called "checks" and "counters".
As people stated before, Mega Amphy and Mega Aero are probably the closest pokes considered "counters" due to their Flying Resist and overall great bulk. Other than that, it's ability to go easily as mixed, not be worn down by SR and such a selective speed tier (I've been seeing a buttload of Noivern for the simple reason that it sits 2 base points higher in speed and can hit hard with Specs) that it makes for an unhealthy meta game. I saw a comment about letting "great" pokes like Jolteon come into the light so Torn-T is making the meta more healthy.
If you are forced to use Jolteon for the simple fact that it's a flying resist (which we just banned Staraptor for let me remind you) and is faster than the hell bird, then you are using a very specific poke to counter a broken threat.
PS. Torn-T gets Iron Tail...
252 Atk Tornadus-T Iron Tail vs. 4 HP / 0 Def Mega Aerodactyl: 208-246 (68.8 - 81.4%) -- 50% chance to OHKO after Stealth Rock
252 Atk Tornadus-T Iron Tail vs. 120 HP / 0 Def Mega Aerodactyl: 208-246 (62.8 - 74.3%) -- guaranteed 2HKO after Stealth Rock
without life orb, let me remind you.