Morgana has 3 damage spells.
And while some do more damage than others,it still helps her to level through the game a lot smoother.
And Karmas damage scales more smoothly not just because her W deals at least some damage,but also because her Q scales with her R.
Though karma could also benefit from a gameplay rework,she currently feels kinda dull,but that might be just my opinion.
And while Zilean usually throws 2 bombs,its still the same spell,meaning that this one spell has to be so strong that it makes up Zileans whole damage throughout the game.
After all you can use the double-bomb attack quite early as well,meaning that it has to be taken into account over the course of the whole game.
Also I'd say that Zilean feels overall rather clunky.
You play this powerful time mage and then spent the rest of the game throwing bombs around like you are Ziggs.