I tried to make a point regarding this before, but no one responded to it (come on, guys, you make me feel bad). My point being, that saying Tornadus-T needs rain support isn't an entirely true statement. The relationship between Tornadus-T and Politoed is mutually symbiotic; Politoed gives Tornadus-T access to his most powerful STAB, and in return, Tornadus-T gives Politoed, and every other member of his team, easy access to momentum. Want to change Tornadus-T's weather to ruin his Hurricanes? You switch in Ninetales, BOOM, he U-turns off you, Regens most of the damage, Politoed comes back in and it's suddenly raining again. Bring in Jirachi to sponge a Hurricane? Again, he bounces off you and brings in something else to deal with you. And once Tornadus-T has helped his teammates in wearing down your team, he can come back in and clean up what remains, and you'll be hard pressed to stop him.Pretty much all pokemon need support to sweep. Blaziken might have needed Slowbro to sweep, and the swift swimmers needed Rain (aka the same support that Tornadus-T needs) in order to be halfway decent. Lets be clear here, I am not, in any way, shape or form, comparing Tornadus-T to Swift Swimmers, merely pointing out that we have banned many pokemon that require support to sweep, ergo, needing "support" doesn't make Tornadus-T not broken.
This, in my mind, is what makes Tornadus-T so dangerous, and in my humble opinion, broken. Yes, he requires support. But he's not parasitic about it -- he offers plenty of support to his teammates in return, mainly the ability to wear down members of his opponents team through Hurricanes and U-turns, and the ability to bring in any member of his team at almost any time. And after all that, he'll smack around just about every member of your team with Hurricanes.