It's a similar situation that Manaphy was in when he was OU. In this meta, Tornadus-T is S-Tier because generating rain is a trivial enough support condition that it doesn't detract enough from his brokenness. When I see Tornadus-T played well on an opposing team, my entire game becomes all about mitigating or eliminating the Tornadus-T, even to more of an extent than it was about mitigating or eliminating Salamence when he ruled in DPP. "I know it when I see it." is indeed the valid phrase here.