yes, you are right, he has one :)
but at the same time, the moment you activate your ult, a big vrooooom goes across the map and the screen turns dark (for the enemy).
so, at that time teemo can just use for R and he can sit on it, it will usually have enough time to activate from the vrooooooom sound until you dash on him.
but, he can also choose to not sit on his shroom.
so, it becomes a mind game for you to block his blind. Think of it like a coin toss, a 50/50 fight.
Which is why you would like to avoid trying to 1shot him until you get duskblade. And that's why you will just get tiamat, clear the entire wave (assuming no cannon) in a Q passive aa, tiamat, aa (so basically, around 1 second), and then roam around the map.
Winning other lanes for your team ^^ or at least, trying to.
assuming the enemy support is good, noct is very difficult to play in late game (like most assassins), so, you don't want to take gambles like that (1 shotting teemo) or rushing 
. While that item does indeed gives you the ability to kill him if you outplay him.
Tiamat lets you get farm and at the same time, try to make plays across the map, making it a much safer choice ^^
Also, since teemo will be bullying you, starving you out of farm and exp. He should be like 1 or 2 levels up on you (more base stats) to help him survive and have more items/gold. Tiamat just ensures you won't be starving anymore with super fast wave push (you can even take like 3-4 aas from teemo while you clear, and then run away). Also, the active damage and AA reset helps with assassinations ^^
But that's my point. You can defeat meta picks if you understand why your pick is strong and why it can work. As long as you play according to that win condition. I only know a few heroes, so, i can't give advice for udyr or wukong.
But to outright dismiss them as trash from the start and impossible to win or "top lane useless" is kind of bad policy.
And yes, you will lose game when your bot lane gets crushed, but that doesn't always happen. Sometimes its even, sometimes your bot lane wins.
And you have the ability if you choose to play something that can roam (even maokai or malphite can roam, like, recall at 6, roam bot, ult there, and then tp top) to influence other lanes in the even scenario case.
