Ad teemo is viable mid. I do it all the time.

If that your feeling on meta, please never play ranked games again. Mid sivir... horrible.

Imma hit you with some knowledge:
AP goes mid because of minions
AP is too squishy to go any other lane

Please learn this, then play ranked.

It's okay. I love playing mid talon, but never get a chance to because people rage if you suggest it. But that aside i destroy casters in mid (cept xerath... **** armor)

Sivir works mid I guess but aside from cait vs certain mages, the mages win every time, Also mages go solo because they count early-mid game on level based base dmg on their spells to do damage and AD caries count on their farm to itemize quickly to do well (Just think a 1650 BF sword is a 35-45% damage increase on reliable autoattacks while a 1600 Rod is 80AP, like 30-60 dmg increase on spells that have CD). so they go bottom with a support so they cam farm without the fear of irreparable harass that mages have. It's not just "the meta" there's a reason it works