He's not too squishy for the top lane. He sacrifices durability for escape options and sheer damage output from range.
He's not too weak for the midlane. He just gets caught by spells rather easily and his own don't do much to hinder the farming potential of other midlaners going into the middle and late game.
You probably shouldn't be playing him as an ADC anyways.
"Support" Teemo only exists to troll enemy ADCs and steal kills from your own.
Teemo in the jungle is a gimmick pick. Worked alright with Feral Flare, but in all honesty is just bad considering his mana costs from spamming Q hurt early.
His kit isn't outdated, he's just got a very specific focus. He's there to shut down melee top laners at the expense of not really bringing more than a meh amount of utility and a healthy amount of burst damage to a fight. And for that, he excels. He also makes up for what he lacks in durability with global map awareness that every other champ only WISHES they could have through his long lasting ward shrooms, which can actually turn the tide of a fight if used correctly and make him a bit of a terror in a 1v1 if you're stupid enough to let him kite you.
Your entire argument is like trying to say Veigar's outdated because he's squishier than other mids but doesn't have the kind of mobility they do. Sure, he doesn't bring the most utility to a teamfight outside of his stun, but if you fulfill the conditions that are incredibly easy for him to set up you aren't getting away from him without having to wait on a respawn timer.
