Trust me, you wouldn't have wanted to face Zorn & Toth on story mode in their initial incarnation. People would be up in arms! Letting people test on the PTS helped a lot with the balancing which makes the new zone, imo, a heck of a lot of fun.
Killed them in story mode in their initial version, and in hard mode. It was a pain in the butt, don't get me wrong, but it was very fun. They nerfed these bosses way too much.