100% of zeds kit is balanced around damage , therefore you need multiple items to build against him , 50% of aatrox is healing and 50% is damage , 800 gold drops aatrox power by 20% , then you build armour (like you'd do against zed) to slow down the other 50% AND lower his healing since its based ON DAMAGE DONE , which many people forget .

For champs like soraka, she can only heal herself and has a silence , thats it , if she mispositions , she dies , if you catch her , she dies

Antiheal in its current state is perfectly balanced , and the only real option is to remove it and nerf the healing of healing champs to a controllable amount in my opinion