People easily jump to conclusions using theory only.
People could easily say that DFT is good on teemo because of the DoT. Just like how they overestimated Rageblade on Teemo, just because he once was good with malady. Teemo can proc DFT only with his high cd blind and his mushrooms, which get removed too easily now due to the reduced duration, smite true sight and sweepers. DFT rarely ever procs. Besides it scales largely with AD and AP, and a good Teemo build doesn't have any, it is even more useless because of the reduced effect due to DoT.
But to be fair it would have been good on Teemo if not for op brand making this mastery op af, leading to its nerf on DoT and AoE.
Thunderlords on the other hand is simply op right now. Secondly Teemo was having trouble trading with many other top laners lately, thunderlords makes up for that.