Janna & Ahri need nerfs.
These solo Q favorite are too safe.
Janna's problem is too much power post laning phase. She either needs to be punished harder in lane or have her utility/scaling lessened later in the game.
Ahri is too safe in lane phase. Safety is fine, but then a champ needs to pay for it by either having less sustain (e.g. 
VERY safe, yet has zero sustain) or less wave clear. Ahri clears entire waves in with 2 Q's...while healing off these Q's and gaining mobility (i.e. survivability) from them.
Maybe that is Ahri's fundamental problem: too much power is put into her Q. It gives her waveclear, sustain, and mobility...i.e., survivability, which is paramount in the very fragile and gankable short mid lane of solo Q.
