Taliyah
Ok.
It is pretty obvious that she is weak right now.
Riot, hear me on this.
She needs buffs, but not to her damage.
Look at the potential damage she has on one rotation.
If you land all your spells correctly, you can potentially deal 1280 (+3.2 AP) magic damage in a single rotation, and most of that can hit multiple targets.
For comparison, Leblanc can do a maximum of 1435 (+3.6 AP) in one rotation, assuming she uses the Q form of her ult and waits for her chain to pop, and most of this is only dealt to a single target.
She needs buffs to her usability. Among other things, her Q could do with a higher rate of fire and she shouldn't be kicked off of her wall from damage below a certain threshold; her wall happening to pass over a Morgana pool and kicking her off in the middle of the enemy team is a horrible situation.