The preseason 5 discussion is missing one crucial thing

A buff for Zac. The cost on his abilities is way too punishing - and the random nature of his blobs just compound on that. Taking 12% of your current health for an engage, but being able to heal 12% of your total health seems like a good idea on paper, but the random nature of the blobs often means if you want to stick to the fight, you have to forsake at least some of that health.

There are plenty of other champions that do his job better. At the time, there are 4 other champions that use their health as a resource for their abilities, and each of them has a far stronger compensation mechanic to counter their health costs, granted, some are a little more forgiving then others, but yeah.

The nerf to his bloblet pickup following his LCS stomping put him in an area where he's not doing okay in. Enemies have more counterplay on his blobs, which again is a good thing on paper, but being a health based champion with a fairly heavy health cost curve with far easier counterplay to his health compensation mechanic then his colleagues (like Mundo, Vlad, Aatrox, and Morde) just makes him a trash tier champion. He doesn't have to be the God tier LCS stomper he used to be to still be a useful champion.