TBH, I would respond to all ur comments, but you have some good points and some bad. I do agree that teemo mushrooms should stack (to about 3 stacks), but they should remain at their damage. Its OP early game, and it's reveal/slow is too strong. Of all ur gap closers, you see how many of them were ranged AD? 3. Trist/Corki/Ezreal. Ezreal is possibly in worse shape than teemo. And while Corki and Trist are strong, their gap closer is often used as an escape mechanism.
Ranged AD aren't supposed to have gap closers like Lee Sin, because they aren't melee.
Also, I wanted to note that Teemo is still played competitively, but as a counter pick to melee champs (especially stomps Trynd).