I think I'll throw my hat in the ring here for Tornadus-T being A-Rank, though not without some hesitation. The reason for this is that Tornadus-T is kind of an anomalous pokemon; it has some worrying weak points, while simultaneously having some ridiculous strengths. For example:
Strengths:
-Powerful STAB Hurricane
-Wallbreaking with Superpower
-Regenerator
-U-turn
-Blazing fast 121 speed
-Nice support options (Taunt and Rain Dance mainly)
Weaknesses:
-Dependence on rain to function consistently
-Generally sparse movepool, making it predictable
-Stealth Rock weakness, essentially stripping it of Regenerator
-Has no reliable option to deal damage outside of it's preferred weather
I'm not sure if the above is all completely accurate (the weaknesses in particular as I'm kind of belting this out on the fly), but I generally feel that Tornadus-T requires a bit too much support to work at maximum effectiveness to be S-Tier. You say Torn-T has regenerator? I say Stealth Rock. You say Torn-T has Uber wallbreaking Hurricane/ Superpower combo? I say Jirachi, Chansey, Rotom-W and Gastrodon are capable of walling it (to an extent, as none are 2hko'd by either move). I say that Tyranitar, Hippowdon and Ninetales exist, and you cannot guarantee rain. I also say Choice Scarf and Priority.
Don't get me wrong. Tornadus-T is absolutely amazing, and under the right conditions - that is, no SR and Drizzle up - I think it's pretty broken. But the definitions are also pretty clear, and Tornadus-T requires no small amount of support. Keep in mind that drizzleToed is actually a massive support requirement, as it automatically forces you into building a rain team - and honestly, any non-Hurrispam Torn-T isn't very good. Trust me, I've tried it, and I tried hard. But outside of rain, Tornadus-T is just underwhelming.
By the by, I was under the impression that Drizzle would be on the table next anyway? In any case, if drizzle did get suspected, then Tornadus-T is obviously not even close to S-Rank.
EDIT: to the poster above: There's also a reason why the competitive community calls Focus Blast 'Focus Miss'. Yes, it's good enough that people use it; but notice that there aren't a lot of pokes in the top twenty or so that rely on it. 70% accuracy is shaky no matter how you slice it, and if Hurricane should so miss for Torn-T outside of rain - then generally it's frail enough that it'll probably die because of it. Not saying that you can't use Hurricane outside of rain - you certainly can, and often it's worth the risk - but should an S-Tier poke really have to take that kind of risk? Mmmmm. :p
It's not "only" Focus Blast and it's not because some people call it Focus Miss because they find it hilarious that it makes this move bad.
Gengar and RP Landorus use it by the way, and the latest in one of the biggest threat right now in OU.
Stone Edge is 10% over it as I said, Specs Toed spams a 80% move called Hydro Pump.
On the other hand Tornadus-T spams a spell that is AT LEAST half time 70% and half time 100 so... yes I'm a genius it's a 85% move on average which is higher than 80 (I'm really a genius).
So just saying, there are TONS of pokemons that rely on an accuracy move lower than 85%, this argument is now cleaned I hope.
And if you tell me that Sun teams are here and lower the accuracy, I'll just say that you can still use Heat Wave, and turn the weather to Rain, or U-Turn to a counter like Dugtrio who traps almost anything in a Sun team. Moreover even with the Sun Presence it's something like 10% on the suspect (you talked about competitive players right?) so who cares, it would lower the accuracy to something still above of 80% (let's say 50% rain, 40% weatherless/sand/hail and 10% Sun, in the end the accuracy is around 83%).
To sum up, you did not really understand what I was explaining (maybe it's my fault), I was doing a comparison, not saying that's it's the same. And as FaceFaceFace pointed out, you can still U-Turn and trap 2/3 of the other weather introducers (the most used ones). Moreover you trap Jirachi for instance.
Gastrodon can't take 2 Specs Hurricane by the way, it's a sure 2HKO. And you even forgot Zapdos and Thundurus-T in the possible counters (Thundurus-T in a more offensive way since he can set up Agility and 0HKO for instance).
And just saying a S rank got weaknesses is obvious, and most of the people here know this. FaceFaceFace explained it better than me.
But the weaknesses you pointed were not all relevant and don't prevent Tornadus-T from claiming the S rank.
EDIT: to the following posts I see, stop picking up a single sentence and complain about it, he's just taking examples, debating on one of them is sterile.