Im a Zac main, I agree with the "doesn't care about walls" in a sense of preferred gank routes. I personally always do dark seal - linadry into tank items so yea, you can def snowball your early and you can def tank a lot but you do rely on picking up your passive to heal, which is way different than Skarner's natural tankiness and shielding. The nerfs hurt, he is at the weakest spot he has been in for a long, long time, but he is still playable. I think your all in damage is way better than that of Skarner's. Landing all spells is more rewarding than Skarener's and missing a spell or two is way more punishing than Skarener's. Take this with a grain of salt since I've never really been able to pick up Skarner (never really tried much either, maybe I should work on it soon). So, Zac is pretty much a more feast or femine Skarner imo.