For swain, every ability except his ult cost nothing in mana. And then when he has his ult, the only thing to stop him is grevious wounds but for morello he has to be below 35% hp which is almost impossible to do to him when he finishes spirit visage.
Zed is just zed. I used to be able to deal with him but now he's just ridiculous. I think you should look at his ultimate because it is the most high reward for low risk thing in his kit. Mid and late game a single ult e q combo will basically guarantee a kill on an adc or other carries and he's extremely safe during the whole process.